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                                                                  Exhibit 10.107
                                 NAVAJO PROJECT
                              CO-TENANCY AGREEMENT

                                      AMONG

                          ARIZONA PUBLIC SERVICE COMPANY

                          DEPARTMENT OF WATER AND POWER
                           OF THE CITY OF LOS ANGELES

                              NEVADA POWER COMPANY

                         SALT RIVER PROJECT AGRICULTURAL
                          IMPROVEMENT AND POWER DISTRICT

                          TUCSON GAS & ELECTRIC COMPANY

                          THE UNITED STATES OF AMERICA

                                                                   DWP No. 10498

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                                 NAVAJO PROJECT
                              CO-TENANCY AGREEMENT

                                TABLE OF CONTENTS
<TABLE>
<CAPTION>

SECTION                                TITLE                                    PAGE
<S>                  <C>                                                        <C>
           1.        PARTIES                                                      1
           2.        RECITALS                                                     1
           3.        AGREEMENT                                                    4
           4.        EFFECTIVE DATE                                               4
           5.        DEFINITIONS                                                  4
                     5.1      Accounting Practice                                 4
                     5.2      Arizona Water Permit                                4
                     5.3      Ash Disposal Area                                   5
                     5.4      Auditing Committee                                  5
                     5.5      Capacity                                            5
                     5.6      Capital Additions                                   5
                     5.7      Capital Betterments                                 5
                     5.8      Capital   Improvements                               6
                     5.9      Capital Replacements                                6
                     5.10     Coal Supply Agreement                                6
                     5.11     Component of the Transmission System                6
                     5.12     Conditional Partial Assignment                      6
                     5.13     Contracting Officer                                  6
                     5.14     Contracts   for Interim Sale of United
                              States' Entitlement                                7
                     5.15     Coordinating Committee                              8
                      5.16     Co-Tenants                                          8
                     5.17     Date of Firm Operation                              8
                     5.18     Energy                                              8
                      5.19     Generation Entitlement Share                        8
                     5.20     Incremental Series Capacitors                       9
                     5.21     Indenture of Lease                                  9
                     5.22     Memorandum Transmission Agreement                   9
                     5.23     Navajo Generating Station                           9
                     5.24     Navajo Plant Site                                   9
                     5.25     Navajo Project                                     10
                     5.26     Navajo Tribe                                       10
                     5.27     Net Effective Generating Capability                10
                     5.28     Operating Agent                                    10
                     5.29     Participants                                       10
                     5.30     Participation Agreement                            10
                     5.31     Power                                               10
                     5.32     Project Agreements                                 10
                     5.33     Project Series Capacitors                          11
                     5.34     Project Manager                                     11
                     5.35     Pumping Plant Site                                 12
</TABLE>

                                       i

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Navajo Project
Co-Tenancy Agreement
Table of Contents

<TABLE>
<CAPTION>

SECTION                                 TITLE                                    PAGE
<S>                   <C>                                                       <C>
                     5.36     Rail Loading Site                                  12
                     5.37     Railroad                                           12
                     5.38     Secretary                                          12
                     5.39     Section 323 Grants                                 12
                     5.40     Southern Transmission System                       12
                     5.41     Station Engineering and Operating Committee        12
                     5.42     Station Work                                       12
                     5.43     Transmission System                                 13
                     5.44     Transmission Engineering and Operating Committee   13
                     5.45     Transmission Work                                  13
                     5.46     Units of Property                                   13
                     5.47     Water Service Contract                             13
                     5.48     Water Service Contract Assignment                  13
                     5.49     Western Transmission System                         14
           6.        OWNERSHIPS AND TITLES                                       14
           7.        ENTITLEMENT TO NAVAJO GENERATING   STATION
                      CAPACITY AND ENERGY                                       19
           8.        USE OF THE TRANSMISSION SYSTEM                              19
           9.        ADMINISTRATION                                              23
          10.        NONPARTITIONMENT                                            28
          11.        MORTGAGE AND TRANSFER OF INTERESTS                          29
          12.        RIGHT OF FIRST REFUSAL                                      32
          13.        DESTRUCTION                                                 36
          14.        SEVERANCE OF IMPROVEMENTS                                   38
          15.        CAPITAL IMPROVEMENTS                                        38
          16.        INTERESTS HELD FOR THE USE AND BENEFIT OF
                      THE UNITED STATES                                          39
          17.        REIMBURSEMENT FOR COSTS AND EXPENSES                        42
          18.        DEFAULTS AND COVENANTS REGARDING OTHER AGREEMENTS           42
          19.        ARBITRATION                                                 48
          20.        ACTIONS PENDING RESOLUTION OF DISPUTES                      52
          21.        TERM AND RIGHTS OF CO-TENANTS UPON TERMINATION              53
          22.        COVENANTS RUNNING WITH THE LAND                             54
           23.        RELATIONSHIP OF PARTICIPANTS                                55
          24.        FEES                                                        56
          25.        UNCONTROLLABLE FORCES                                       56
          26.         GOVERNING LAW                                               57
          27.        BINDING OBLIGATIONS                                         57
          28.        NONDEDICATION OF FACILITIES                                 58
          29.        ENVIRONMENTAL PROTECTION                                    58
          30.        ASSIGNMENT OF INTERESTS                                     62
          31.        USE OF FACILITIES OF LOS ANGELES                            62
</TABLE>

                                        ii


<PAGE>

Navajo Project
Co-Tenancy Agreement
Table of Contents

<TABLE>
<CAPTION>

SECTION                                TITLE                                       PAGE
<S>                  <C>                                                            <C>
          32.        NOTICES                                                        63
          33.        MISCELLANEOUS PROVISIONS CONCERNING THE PROJECT AGREEMENTS     64
          34.        NAVAJO PROJECT GENERAL CONTRACT PROVISIONS                      67
          35.        COMPLIANCE WITH COMPACTS                                       67
</TABLE>

EXHIBITS

     A         NAVAJO GENERATING STATION

B & B-B        TRANSMISSION SYSTEM

     C         NAVAJO PROJECT GENERAL PROVISIONS

                                       iii


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                                 NAVAJO PROJECT
                              CO-TENANCY AGREEMENT

1.     PARTIES: The parties to this Co-Tenancy Agreement are: THE UNITED STATES
      OF AMERICA, hereinafter referred to as the "United States", acting through
      the Secretary of the Interior, his duly appointed successor or his duly
      authorized representative; ARIZONA PUBLIC SERVICE COMPANY, an Arizona
      corporation, hereinafter referred to as "Arizona"; DEPARTMENT OF WATER AND
      POWER OF THE CITY OF LOS ANGELES, a department organized and existing
      under the Charter of the City of Los Angeles, a municipal corporation of
      the State of California, hereinafter referred to as "Los Angeles"; NEVADA
      POWER COMPANY, a Nevada corporation, hereinafter referred to as "Nevada";
      SALT RIVER PROJECT AGRICULTURAL IMPROVEMENT AND POWER DISTRICT, an
      agricultural improvement district organized and existing under the laws of
      the State of Arizona, hereinafter referred to as "Salt River Project"; and
      TUCSON GAS Section ELECTRIC COMPANY, an Arizona corporation, hereinafter
      referred to as "Tucson".

2.     RECITALS: This Co-Tenancy Agreement is made with refer ence to the
      following facts, among others:

            2.1 By the Colorado River Basin Project Act (82 Stat. 885) the
      Congress of the United States authorized the construction, operation and
      maintenance of the

                                       1
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       Central Arizona Project. Pursuant to Section 303 of said Act, the
      Secretary is authorized to enter into agreements with non-Federal
      interests proposing to construct thermal generating Power plants whereby
      the United States shall acquire the right to such portions of their
      Capacity, including the delivery of Power and Energy over the appurtenant
      transmission facilities to mutually agreed upon delivery points, as he
      determines are required in connection with the operation of the Central
      Arizona Project.

            2.2 The Secretary has determined that the acquisition of a right to
      a portion of the Capacity of the Navajo Project is the most feasible plan
      for supplying the Power requirements of the Central Arizona Project and
      augmenting the Lower Colorado River Basin Development Fund.

            2.3 As of September 30, 1969, the Participants and Southern
      California Edison Company entered into the Memorandum Transmission
      Agreement (Contract No. 14-06-300-2140), which establishes the terms and
      conditions for the interconnection of the Transmission System at Moenkopi
      Switchyard with the existing 500 kv transmission line from the Four
      Corners Generating Station to the Eldorado Substation. These terms and
      conditions are to be the basis for a more definitive agreement.

            2.4 As of September 29, 1969 the Co-Tenants and the Navajo Tribe
      entered into the Indenture of Lease

          

                                        2


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      wherein the Co-Tenants leased the Navajo Plant Site, Pumping Plant Site,
      Ash Disposal Area, Rail Loading Site, and certain related rights on
      certain real property located within the Navajo Reservation.

             2.5 By the provisions of said Indenture of Lease, approval was
      obtained from the Navajo Tribe for the grants by the Secretary of
      rights-of-way for a railroad, coal conveyor and portions of the
      Transmission System. Such approval was also obtained by way of a
      resolution from the Hopi Tribal Council.

            2.6 The Participants entered into the Participation Agreement,
      which provides the basic principles for their participation in the Navajo
      Project. These principles are intended to be the basis of more
      definitive agreements, including this Co-Tenancy Agreement.

            2.7 As of January 17, 1969, Salt River Project entered into a Water
      Service Contract with the United States (Contract No. 14-06-400-5033),
      relating to the diversion and consumptive use of specified amounts of
      water annually. In addition, the Arizona Water Permit was issued by the
      State Land Commissioner of the State of Arizona on September 4, 1969,
      granting to the Salt River Project a permit to appropriate and use a
      specified amount of water in conjunction with the operation of a thermal
      electric generating plant. By a Water Service Contract Assignment dated
      as of December 22, 1969, Salt


                                       3


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      River Project assigned to the Co-Tenants undivided interests in the Water
      Service Contract and the Arizona Water Permit.

            2.8 As of June 1, 1970, the Co-Tenants entered into the Coal Supply
      Agreement with Peabody Coal Company, relating to a supply of coal for the
      Navajo Generating Station.

            2.9 The Participants desire by this Co-Tenancy Agreement to
      establish terms and conditions relating to their interests in and their
      ownership of the Navajo Project and to establish certain rights and
      obligations under the Project Agreements.

3.     AGREEMENT: The Participants agree as follows:

4.     EFFECTIVE DATE: This Co-Tenancy Agreement shall become effective when it
      has been duly executed and delivered on behalf of all the Participants.

5.     DEFINITIONS: The following terms, when used herein, shall have the
      meanings specified:

            5.1 ACCOUNTING PRACTICE: Generally accepted accounting principles,
      in accordance with the Federal Power Commission's "Uniform System of
      Accounts Prescribed for Public Utilities and Licensees (Class A and Class
      B)", in effect on January 1, 1970, and as such system of accounts may be
       amended from time to time.

            5.2 ARIZONA WATER PERMIT: Permit No. A-3244 issued by the State Land
      Commissioner of the State of



                                       4


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      Arizona on September 4, 1969, granting to the Salt River Project a permit
      to appropriate and use water in conjunction with the operation of a
      thermal electric generating plant, which said permit has a priority date
      of December 18, 1964.

            5.3 ASH DISPOSAL AREA: The area for the disposal of ash resulting
      from the operation of the Navajo Generating Station described on Exhibit 4
      to the Indenture of Lease.

            5.4 AUDITING COMMITTEE: A committee established pursuant to and
      which will exercise the functions described in the Project Agreements.

            5.5 CAPACITY: Electrical rating expressed in megawatts (mw) or
      megavolt-amperes (mva).

            5.6 CAPITAL ADDITIONS: Any Units of Property, land or land rights
      which are added to the Navajo Project and which do not substitute for any
      existing Units of Property, land or land rights constituting a part of the
      Navajo Project, and which in accordance with Accounting Practice would be
      capitalized.

            5.7 CAPITAL BETTERMENTS: The improvement of land or land rights or
      the enlargement or improvement of any Units of Property constituting a
      part of the Navajo Project or the substitution thereof, where such
      substitution constitutes an enlargement or improvement as compared with
      that for which it is substituted, which

                                      -5-


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      in accordance with Accounting Practice would be capitalized.

            5.8 CAPITAL IMPROVEMENTS: All or any Capital Additions, Capital
      Betterments, or Capital Replacements.

            5.9 CAPITAL REPLACEMENTS: The substitution of any Units of Property
      for other Units of Property constituting a part of the Navajo Project,
      where such substitution does not constitute an enlargement or improvement
      of that for which it is substituted, which in accordance with Accounting
      Practice would be capitalized.

            5.10 COAL SUPPLY AGREEMENT: The Navajo Station Coal Supply Agreement
      entered into as of June 1, 1970, by and between Peabody Coal Company and
      the Co-Tenants, relating to a supply of coal for the Navajo Generating
      Station.

            5.11 COMPONENT OF THE TRANSMISSION SYSTEM: Any of the components of
      the Transmission System as described in Exhibit B hereto.

            5.12 CONDITIONAL PARTIAL ASSIGNMENT: An assignment which the
      Co-Tenants may obtain from Peabody Coal Company covering the coal areas
      dedicated under the terms and conditions of the Coal Supply Agreement.

            5.13 CONTRACTING OFFICER: The Secretary, his duly appointed
      successor or his duly authorized representative.

            5.14 CONTRACTS FOR INTERIM SALE OF UNITED STATES'

                                      -6-


<PAGE>

      ENTITLEMENT: The contracts by which the United States has contracted with
      other Participants and Southern California Edison Company for the interim
      sale of United States' entitlement of Navajo Project until required for
      other purposes of the Colorado River Basin Project Act. These contracts
      are:

                  5.14.1 Contract with Department of Water and Power of the City
            of Los Angeles for Interim Sale of United States' Entitlement of
            Navajo Project, Contract No. 14-06-300-2133, dated as of September
            30, 1969;

                  5.14.2 Contract with Nevada Power Company for Interim Sale of
            United States' Entitlement of Navajo Project, Contract No.
            14-06-300-2134, dated as of September 30, 1969;

                  5.14.3 Contract with Southern California Edison Company for
            Interim Sale of United States' Entitlement of Navajo Project,
            Contract No. 14-06-300-2135, dated as of September 30, 1969;

                  5.14.4 Contract with Salt River Project Agricultural
            Improvement and Power District for Interim Sale of United States'
            Entitlement of Navajo Project, Contract No. 14-06-300-2136, dated
            as of September 30, 1969;

                  5.14.5 Contract with Arizona Public Service Company for
            Interim Sale of United States' Entitlement

                                      -7-


<PAGE>

            of Navajo Project, Contract No. 14-06-300-2137, dated as of
            September 30, 1969; and

                  5.14.6 Contract with Tucson Gas Electric Company for Interim
            Sale of United States' Entitlement of Navajo Project, Contract No.
            14-06-300-2138, dated as of September 30, 1969.

            5.15 COORDINATING COMMITTEE: A committee established pursuant to
      and which will exercise the functions described in the Project Agreements.

            5.16 CO-TENANTS: Any one or all of the parties hereto, other than
      the United States.

            5.17 DATE OF FIRM OPERATION: The date established in accordance with
      the Project Agreements on which each unit of the Navajo Generating Station
      is determined by the Station Engineering and Operating Committee to be
      reliable as a source of generation and on which that unit can reasonably
      be expected to operate continuously at its rated Capacity.

            5.18 ENERGY: Kilowatt-hours (kwh).

            5.19 GENERATION ENTITLEMENT SHARE. The percentage entitlement of
      each Participant in each unit of the Navajo Generating Station. Each
      Participant's percentage is as follows:

            5.19.1       Arizona               = 14.0 percent.
            5.19.2       Los Angeles           = 21.2 percent.
            5.19.3       Nevada                = 11.3 percent.

                                      -8-


<PAGE>

            5.19.4       Salt River Project    = 21.7 percent.
            5.19.5       Tucson                =   7.5 percent.
            5.19.6       United States         = 24.3 percent.

            5.20 INCREMENTAL SERIES CAPACITORS: Series capacitors described in
      the Memorandum Transmission Agreement and in any subsequent Project
      Agreement(s) superseding the Memorandum Transmission Agreement which will
      serve the purposes described therein for "incremental series capacitors".

            5.21 INDENTURE OF LEASE: The Indenture of Lease dated as of the 29th
      day of September, 1969, by and between the Navajo Tribe and the
      Co-Tenants.

            5.22 MEMORANDUM TRANSMISSION AGREEMENT: The Memorandum Transmission
      Agreement dated as of the 30th day of September, 1969 (Contract No.
      14-06-300-2140), by and between Southern California Edison Company and the
      Participants.

            5.23 NAVAJO GENERATING STATION: Three coal-fired steam electric
      generating units, to be constructed at the Navajo Plant Site, each having
      a nameplate rating of 750 mw and, subject to final design, an estimated
       Net Effective Generating Capability of 770 mw, and all facilities and
      structures used therewith or related thereto, all as described in Exhibit
      A hereto.

            5.24 NAVAJO PLANT SITE: A parcel of land in Coconino County,
      Arizona, consisting of approximately

                                      -9-

<PAGE>

      1,020 acres, described in Exhibit 2 to the Indenture of Lease.

            5.25 NAVAJO PROJECT: The Navajo Generating Station and the
      Transmission System.

             5.26 NAVAJO TRIBE: The Navajo Tribe of Indians.

            5.27 NET EFFECTIVE GENERATING CAPABILITY: The maximum continuous
      ability of each unit of the Navajo Generating Station to produce Power
      which is available to the Participants at the Navajo 500 kv Switchyard 500
      kv bus.

            5.28 OPERATING AGENT: A Co-Tenant responsible for the operation and
      maintenance of the Navajo Generating Station or a Component of the
      Transmission System in accordance with the Project Agreements.

            5.29 PARTICIPANTS: Any one or more of the parties hereto, including
      the United States.

            5.30 PARTICIPATION AGREEMENT: The Navajo Project Participation
      Agreement, dated as of September 30, 1969 (Contract No. 14-06-300-2131),
      and the Amendment and Supplement #1 thereto dated as of January 16, 1970,
      which provide the basic principles for the Participants' participation in
      the Navajo Project.

            5.31 POWER: Kilowatts (kw) or megawatts (mw).

            5.32 PROJECT AGREEMENTS: This Co-Tenancy Agreement, the
      Participation Agreement, the grants from the United States for
      rights-of-way across Indian lands pursuant

                                      -10-


<PAGE>

       to 2S U.S.C. Section 323, the Navajo Project Power Coordination Agreement,
      the Southern Transmission System, Western Transmission System and Navajo
      Generating Station Construction Agreements, the Southern Transmission
      System, Western Transmission System and Navajo Generating Station
      Operating Agreements, other grants of rights-of-way and easements for
      Navajo Project facilities, the Indenture of Lease, the Arizona Water
      Permit, the Water Service Contract, the Water Service Contract Assignment,
      the Coal Supply Agreement, the Conditional Partial Assignment, the
      Multi-Party Agreement, the Memorandum Transmission Agreement, and such
      other agreements as the Participants find necessary or desirable and
      designate as Project Agreements, as such Project Agreements are originally
      executed or as they may thereafter be supplemented, amended or superseded;

            5.33 PROJECT SERIES CAPACITORS: Series capacitors described in the
      Memorandum Transmission Agreement and in any subsequent Project
      Agreement(s) superseding the Memorandum Transmission Agreement, which will
      serve the purposes described therein for "project series capacitors".

            5.34 PROJECT MANAGER: A Co-Tenant responsible for the construction
      and completion of the Navajo Generating Station or a Component of the
      Transmission System in accordance with the Project Agreements.

                                      -11-

<PAGE>

            5.35 PUMPING PLANT SITE: The site for facilities to divert and pump
      water from Lake Powell, including water intake works, pumping station,
      water lines and related facilities, as described on Exhibit 2 to the
      Indenture of Lease.

            5.36 RAIL LOADING SITE: The site for the conveyor termination and
      rail loading facilities, related facilities and equipment and coal storage
      as described on Exhibit 3 to the Indenture of Lease.

            5.37 RAILROAD: The railroad described in Exhibit A hereto.

            5.38 SECRETARY: The Secretary of the Interior.

            5.39 Section 323 GRANTS: Grants of easements and rights-of-way by
      the United States to the Co-Tenants, covering the Navajo Plant Site, the
      Ash Disposal Area, the Pumping Plant Site, the Railroad right-of-way, the
      Rail Loading Site and related rights.

            5.40 SOUTHERN TRANSMISSION SYSTEM: The Southern Transmission System
      as described in Exhibit B hereto.

            5.41 STATION ENGINEERING AND OPERATING COMMITTEE: A committee
      established pursuant to and which will exercise the functions described
      in the Project Agreements.

            5.42 STATION WORK: Engineering, design, contract preparation,
      purchasing, construction, supervision, expediting, inspection,
      accounting, testing, start-up, protection, operation, repair,
      maintenance, replacement, or

                                      -12-


<PAGE>

      reconstruction, of or for the Navajo Generating Station.

            5.43 TRANSMISSION SYSTEM: The Transmission System as generally
      described in Exhibit B hereto.

            5.44 TRANSMISSION ENGINEERING AND OPERATING COMMITTEE: A committee
      established pursuant to and which will exercise the functions described in
      the Project Agreements.

            5.45 TRANSMISSION WORK: Engineering, design, contract preparation,
      purchasing, construction, supervision, expediting, inspection,
      accounting, testing, protection, operation, repair, maintenance,
      replacement, or reconstruction, of or for the Transmission System.

            5.46 UNITS OF PROPERTY: Units of property as described in the
      Federal Power Commission's "List of Units of Property for Use in
      Connection with Uniform System of Accounts Prescribed for Public Utilities
      and Licensees," in effect on January 1, 1961, and as such list may be
      amended from time to time.

            5.47 WATER SERVICE CONTRACT: The Water Service Contract dated the
      17th day of January, 1969, between the United States and the Salt River
      Project (Contract No. 14-06-400-5033).

            5.48 WATER SERVICE CONTRACT ASSIGNMENT: The Water Service Contract
      Assignment dated as of the 22nd day of December, 1969, between the Salt
      River Project and the other Co-Tenants whereby Salt River Project

                                      -13-
<PAGE>
      assigned undivided interests in the Water Service Contract and the Arizona
      Water Permit to the Co-Tenants.

             5.49 WESTERN TRANSMISSION SYSTEM: The Western Transmission System as
      described in Exhibit B hereto.

6.     OWNERSHIPS AND TITLES:

            6.1 The Co-Tenants shall acquire and own undivided interests as
      tenants in common in the Navajo Generating Station, the Water Service
      Contract, the Arizona Water Permit, the Coal Supply Agreement, the
      Conditional Partial Assignment, and those Project Agreements relating to
      land and land rights for the Navajo Generating Station to which the United
      States is not a party in its capacity as a Participant, as follows:

            6.1.1        Arizona          = 14.0%

            6.1.2        Los Angeles      = 21.2%

            6.1.3        Nevada           = 11.3%

            6.1.4        Salt River
                             Project     = 21.7% for its own use and benefit

                                     and   24.3% for the use and benefit of the
                                                United States in accordance with
                                                Project Agreements

            6.1.5        Tucson           =   7.5%

            6.2 The Co-Tenants shall acquire and own undivided interests as
      tenants in common in the Components of the Transmission System as follows:

                                      -14-
<PAGE>

            6.2.1 Navajo 500 kv Switchyard

                  Navajo-Moenkopi 500 kv line

                  (i)    Arizona          = 14.0%

                  (ii)   Los Angeles      = 21.2%

                  (iii) Nevada           = 11.3%

                  (iv)   Salt River
                             Project     = 21.7% for its own use and benefit and

                                          24.3% for the use and benefit of the
                                                 United States in accordance with
                                                Project Agreements.

                  (v)    Tucson           =   7.5%

            6.2.2 Navajo-Westwing 500 kv line

                   Moenkopi-Westwing 500 kv line

                  Westwing 500 kv Switchyard

                  (i)    Arizona          = 24.7%

                  (ii)   Salt River
                             Project     = 38.3% for its own use and benefit and

                                           23.7% for the use and benefit of the
                                                United States in accordance with
                                                Project Agreements.

                  (iii) Tucson            = 13.3%

            6.2.3 Westwing Substation 2-1332 MVA 500/230 kv transformer banks
                  and transformer leads and spare 444 MVA 500/230 kv transformer
                  and transformer leads

                  (i)    Arizona          = 28.5%

                                      -15-
<PAGE>

                  (ii)   Salt River
                             Project     = 44.2% for its   own use and benefit and

                                          27.3% for the use and benefit of the
                                                 United States in accordance with
                                                Project Agreements.

            6.2.4 Westwing Substation 600 MVA 500/345 kv transformer bank and
                  transformer leads and spare 200 MVA 500/345 kv transformer and
                  transformer leads

                  (i)    Arizona          = 19.5%

                  (ii)   Tucson           = 80.5%

            6.2.5 Westwing 230 kv Switchyard

                  (i)    Arizona          = 39.9%

                  (ii)   Salt River
                             Project     = 44.9% for its own use and benefit and

                                          15.2% for the use and benefit of the
                                                 United States in accordance with
                                                Project Agreements.

                  Upon completion of the United States' two 230 kv lines to the
                  reserved bay positions in the Westwing 230 kv Switchyard, (i)
                  and (ii) of this Section 6.2.5 shall be as follows:

                  (i)    Arizona          = 32.1%

                  (ii)   Salt River
                             Project     = 36.1% for its own use and benefit and

                                           31.8% for the use and

                                      -16-
<PAGE>

                                                benefit of the United States in
                                                accordance with Project
                                                Agreements.

            6.2.6 Other Associated Components of the Southern Transmission
      System, as described in paragraph F of Exhibit B hereto, shall be solely
      owned by Arizona.

             6.2.7 Navajo-McCullough 500 KV line and McCullough Line Compensation

                  (i)    Los Angeles      = 48.9%

                  (ii)   Nevada           = 26.1%

                  (iii) Salt River
                             Project     = 25.0% for the use and benefit of the
                                                United States in accordance with
                                                Project Agreements.

            6.2.8 McCullough 500 kv Switchyard

                  (i)    Los Angeles      = 74.8%

                  (ii)   Nevada           = 19.0%

                  (iii) Salt River
                             Project     =   6.2% for the use and benefit of the
                                                United States in accordance with
                                                Project Agreements.

            6.2.9 McCullough Substation Common Facilities, as described in
                  Exhibit B hereto.

                  (i)    Los Angeles      = 67.9%

                  (ii)   Nevada           = 23.9%

                  (iii) Salt River
                             Project     =   8.2% for the use and

                                      -17-
<PAGE>

                                                benefit of the United States in
                                                accordance with Project
                                                Agreements.

            6.3 The ownerships and titles described in this Co-Tenancy Agreement
      shall be determined to have vested simultaneously in the Co-Tenants so
      that the estate of each shall be determined to be concurrent as to right
      and priority.

            6.4 Within eighteen (18) months following the Date of Firm Operation
      of the final unit of the Navajo Generating Station placed in operation,
      the Participants shall jointly make, execute and deliver a supplement to
      this Co-Tenancy Agreement in recordable form which shall describe with
      particularity and detail the facilities and other property then
      constituting the Navajo Project not specifically described in the exhibits
      hereto, and such supplement, when recorded, shall be and become a part of
      this Co-Tenancy Agreement.

            6.5 In the event any Participant transfers or assigns any of its
      rights, title or interest in and to the Navajo Project in accordance with
      the terms and conditions of this Co-Tenancy Agreement, the Participants
      and any successor shall jointly make, execute and deliver a supplement to
      this Co-Tenancy Agreement in recordable form which shall describe with
      particularity and detail the rights, titles and interests of each
      Participant and

                                      -18-
<PAGE>

      any successor following such transfer or assignment.

7.     ENTITLEMENT TO NAVAJO GENERATING STATION CAPACITY AND ENERGY:

            7.1 The Capacity entitlement of each Participant in each unit of the
      Navajo Generating Station shall be the product of its Generation
      Entitlement Share and the Net Effective Generating Capability of such
      unit.

            7.2 Each Participant shall be entitled to schedule for its account
      Power and Energy from any generating unit up to the amount of its
      available Capacity entitlement in such unit.

8.     USE OF THE TRANSMISSION SYSTEM:

            8.1 Each Participant shall have the right to use the Transmission
      System to transmit to its designated delivery points under normal
      operating conditions Power in an amount equivalent to the sum of its
      Capacity entitlements in the Navajo Generating Station as provided in
      Section 7 hereof or to reserve the Transmission System for such
      transmission without regard to the origin, source, ownership or type of
      generation used to produce such Power.

            8.2 Any Participant may acquire firm entitlement in the Transmission
      System in addition to that provided for in Section 8.1 hereof upon the
      written agreement of all Participants having cost responsibility under the
      Project Agreements for the facilities over which such

                                      -19-
<PAGE>

      firm entitlement is sought, provided that said firm entitlement does not
      materially interfere with the right of any other Participant to utilize
      its entitlement as provided in Section 8.1 hereof. Such written agreement
      shall specify the amount of monetary compensation to be paid to and the
      allocation among the Participants for such firm entitlement.

            8.3 Any Participant may make non-firm use of transmission Capacity
      in addition to its use under Section 8.1 hereof to the extent that
      transmission Capacity is determined to be available by the Operating Agent
      for that segment of the Transmission System over which the Capacity is
      desired in accordance with criteria to be developed by the Transmission
      Engineering and Operating Committee.

            8.4 If two or more Participants concurrently desire to make non-firm
      use of transmission Capacity in the same segment of the Transmission
      System pursuant to Section 8.3 hereof and the available transmission
      Capacity in such segment is not adequate to satisfy all such requests,
       then, unless otherwise agreed, the available Capacity will be shared by
      those Participants concurrently requesting such Capacity in proportion to
      their cost responsibility in such segment as provided in the Project
      Agreements.

             8.5 The Participants' designated points of

                                      -20-
<PAGE>

      delivery shall be as follows:

                  8.5.1 Arizona       =   Navajo 500 kv Switchyard and Westwing
                                         Substation.

                  8.5.2 Los Angeles   =   Navajo 500 kv Switchyard and McCullough
                                        500 kv Switchyard.

                  8.5.3 Nevada        =   Navajo 500 kv Switchyard and McCullough
                                         500 kv Switchyard.

                  8.5.4 Salt River    =   Navajo 500 kv Switchyard and Westwing
                             Project     Substation.

                  8.5.5 Tucson        =   Navajo 500 kv Switchyard and Westwing
                                         Substation.

                  8.5.6 United        =   Navajo 500 kv Switchyard, McCullough
                             States      500 kv Switchyard, Westwing Substation,
                                        and the Moenkopi Switchyard during the
                                        period in which the United States is
                                        selling Power to Southern California
                                        Edison Company pursuant to the Contract
                                        With Southern California Edison Company
                                        for Interim Sale of United States'
                                        Entitlement of Navajo Project for
                                         delivery at Moenkopi Switchyard.

            8.6 Each Participant shall be entitled to interconnect its
      transmission system with the Transmission System at its designated points
      of delivery, and the costs of such interconnection shall be paid by such
      Participant.

            8.7 Upon agreement with all the other Partici-

                                      -21-
<PAGE>

      pants, a Participant may at its expense make interconnections to the
      Transmission System at points other than its designated points of
      delivery. Such agreement shall specify the terms and conditions under
      which such interconnections may be made, the charges, if any, to the
      interconnecting Participant, and the distribution of the proceeds
      therefrom to the other Participants.

            8.8 Unless otherwise agreed by the Transmission Engineering and
      Operating Committee, when the Capacity available to the Participants in
      any segment of the Transmission System is insufficient to accommodate all
      of the firm use of the Transmission System pursuant to Section 8.1 hereof,
      then the use of the available Capacity of that segment of the Transmission
      System will be allocated in proportion to the Participants' cost
      responsibility in such segment. It is not the intention of the
      Participants to dedicate any Capacity in the Transmission System for use
      by other parties.

            8.9 The Transmission System will be interconnected with the Four
      Corners-Eldorado 500 kv line at the Moenkopi Switchyard in accordance with
      the Memorandum Transmission Agreement, and as such agreement may hereafter
      be supplemented, amended or superseded.

            8.10 For the purpose of this Section 8, any use of any section of
      line by the United States which is in excess of the greater of (i) the
      United States' percentage

                                      -22-
<PAGE>

      cost responsibility in such line times the capability of such line, or
      (ii) the capability required to supply the Power requirements of the
      Central Arizona Project, shall be deemed to be non-firm use unless the
      right to such use shall have been acquired pursuant to Section 8.2 hereof.

             8.11 Notwithstanding the provisions of this Section 8, Los Angeles
      shall have the right to use the McCullough Substation or to interconnect
      its transmission system therewith for purposes other than those of the
      Navajo Project established pursuant to the Project Agreements; provided,
      that such use or interconnection shall not unreasonably interfere with the
      rights, titles or interests of the other Participants in the Transmission
      System as established pursuant to Project Agreements.

9.     ADMINISTRATION:

            9.1 As a means of securing effective cooperation and interchange of
      information and of providing consultation on a prompt and orderly basis
      among the Participants in connection with various administrative and
      technical problems which may arise from time to time in connection with
      the terms and conditions of the Project Agreements, the Coordinating
      Committee, Auditing Committee, Transmission Engineering and Operating
      Committee and Station Engineering and Operating Committee, established
      under the provisions of Section 8 of the Participation Agreement, shall
      continue in existence and shall have the

                                      -23-
<PAGE>
      responsibilities set forth in Sections 9.2 through 9.5 hereof.

            9.2 The Coordinating Committee shall be composed of one (1)
      representative of each Participant, who shall be the Contracting Officer
      or an officer or general manager of a Participant or the designee of any
      of the foregoing and shall:

            9.2.1 Provide liaison among the Participants at the management
                  level.

            9.2.2 Exercise general supervision over the Station Engineering and
                   Operating Committee, the Transmission Engineering and
                  Operating Committee, the Auditing Committee and other
                  permanent or ad hoc committees established pursuant to Section
                  9.11 hereof.

             9.2.3 Consider matters referred to it by another committee.

            9.2.4 Perform such other functions and duties as may be assigned to
                  it in the Project Agreements.

            9.2.5 Review, discuss and act upon disputes among the Participants
                  arising under the Project Agreements.

            9.3 The Station Engineering and Operating Committee shall consist of
      two (2) representatives desig-

                                      -24-

<PAGE>

      nated by each Participant, and each such representative shall be
      authorized by the Participant by which he is designated to act on its
      behalf with respect to those matters herein provided to be the
      responsibilities of the Station Engineering and Operating Committee. The
      Station Engineering and Operating Committee shall:

            9.3.1 Provide liaison among the Participants and between them and
                  the Project Manager and the Operating Agent for the Navajo
                   Generating Station with respect to the engineering,
                  construction, operation, maintenance, replacement and
                  reconstruction of the Navajo Generating Station.

            9.3.2 Perform such other functions and duties as may be assigned to
                  it in the Project Agreements or by the Coordinating Committee.

            9.4 The Transmission Engineering and Operating Committee shall
      consist of two (2) representatives designated by each Participant, and
      each such representative shall be authorized by the Participant by which
      he is designated to act on its behalf with respect to those matters herein
      provided to be the responsibilities of the Transmission Engineering and
      Operating Committee. The Transmission Engineering and Operating Committee
      shall:

                                      -25-
<PAGE>
         
            9.4.1 Provide liaison among the Participants and between them and
                  the Project Managers and the Operating Agents for the
                  Components of the Transmission System with respect to the
                  engineering, construction, operation, maintenance, re-
                  placement and reconstruction of the Transmission System.

            9.4.2 Perform such other functions and duties as may be assigned to
                  it in the Project Agreements or by the Coordinating Committee.

            9.5 The Auditing Committee shall consist of two (2) representatives
      designated by each Participant, and each such representative shall be
      authorized by the Participant by which he is designated to act on its
      behalf with respect to those matters herein provided to be the
      responsibilities of the Auditing Committee. The Auditing Committee shall:

            9.5.1 Develop procedures for proper accounting and financial liaison
                  among the Participants in connection with the engineering,
                  construction, operation, replacement, reconstruction and
                  maintenance of the Navajo Project.

            9.5.2 Review accounting and financial

                                      -26-
<PAGE>

                  aspects of the engineering, construction, operation,
                  maintenance, replacement and reconstruction of the Navajo
                  Project.

            9.5.3 Advise and make recommendations to the Coordinating Committee,
                  the Project Managers and the Operating Agents on matters
                   involving auditing and financial transactions.

            9.5.4 Perform such other functions and duties as may be
                  assigned to it in the Project Agreements or by the
                  Coordinating Committee.

          9.6 Any action or determination of a committee must be unanimous.

          9.7 All actions, agreements or determinations made by the committees
      shall be reduced to writing and any such action, agreement or
      determination shall become effective when signed by a representative of
      each Participant on the committee or an authorized alternate. The Station
      Engineering and Operating Committee, the Transmission Engineering and
      Operating Committee and the Auditing Committee shall keep written minutes
      and records of all meetings

          9.8 The committees shall have no authority to modify any of the terms,
      covenants or conditions of the

                                      -27-
<PAGE>

      Project Agreements.

            9.9 If the Station Engineering and Operating Committee, Transmission
      Engineering and Operating Committee or the Auditing Committee fail to
      reach agreement while performing the respective functions and duties
      assigned to them in this Co-Tenancy Agreement or in the other Project
      Agreements, then such disagreement shall be referred to the Coordinating
      Committee.

            9.10 Each Participant shall notify the other Participants promptly
      of any change in the designation of its representatives on the committees.
      A Participant may designate an alternate to act as its representative on
      any committee in the absence of the regular member or to act on specified
      occasions with respect to specified matters. Any alternate representative
      appearing at a committee meeting shall be deemed to have authority to act
      on behalf of the Participant he represents unless he furnishes written
      notice to the committee chairman to the contrary.

            9.11 The Participants, acting through the Coordinating Committee,
      shall have the right to establish permanent or ad hoc committees. The
      authority and duties of any such committee shall be set forth in writing
      and shall be subject to the provisions of the Project Agreements.

10.    NONPARTITIONMENT: The Co-Tenants and each of them accept title to the
      Navajo Project and their rights, titles and

                                      -28-
<PAGE>

      interests in the Project Agreements as tenants in common. Each Co-Tenant
      agrees to waive any rights which it may have to partition the Navajo
      Project, or the Project Agreements, whether by partitionment in kind or by
      sale and division of the proceeds, and further agrees that it will not
       resort to any action in law or in equity to partition the Navajo Project,
      or the Project Agreements, and it waives the benefits of all laws that may
      now or hereafter authorize such partition for a term (i) which shall be
      co-terminus with this Co-Tenancy Agreement, or (ii) which shall be for
      such lesser period as may be required under applicable law.

11.    MORTGAGE AND TRANSFER OF INTERESTS:

            11.1 Except as provided in Section 11.6 hereof, each Co-Tenant shall
      have the right at any time and from time to time to mortgage, create or
      provide for a security interest in or convey in trust all or a part of its
      ownership share in the Navajo Project, together with an equal interest in
      the Project Agreements, to a trustee or trustees under a deed of trust,
      mortgage or indenture, or to a secured party or parties under a security
      agreement, as security for its present or future bonds or other
      obligations or securities, and to any successors or assigns thereof,
      without need for the prior written consent of any other Participant and
      without such mortgagee, trustee or secured party assuming or becoming in

                                      -29-
<PAGE>

      any respect obligated to perform any of the obligations of the
      Participants.

            11.2 Except as provided in Section 11.6 hereof, any mortgagee,
      trustee or secured party under present or future deeds of trust,
      mortgages, indentures or security agreements of any of the Co-Tenants and
      any successor or assign thereof, and any receiver, referee or trustee in
      bankruptcy or reorganization of any of the Co-Tenants, and any successor
      by action of law or otherwise, and any purchaser, transferee or assignee
      of any thereof may, without need for the prior written consent of any
      other Participant, succeed to and acquire all the rights, titles and
      interests of such Co-Tenant in the Navajo Project and the Project
      Agreements and may take over possession of or foreclose upon said rights,
      titles and interests of such Co-Tenant.

            11.3 Except as provided in Section 11.6 hereof, each Co-Tenant shall
      have the right to transfer or assign all or part of its ownership share in
      the Navajo Project, together with an equal interest in the Project
      Agreements, to any of the following without the need for prior written
      consent of any other Participant:

           11.3.1 To any entity acquiring all or substantially all of the
                  property of such Co-Tenant ; or

           11.3.2 To any entity merged or consolidated

                                      -30-
<PAGE>

                  with   such Co-Tenant; or

           11.3.3 To any entity which is wholly-owned by a Co-Tenant; or

           11.3.4 To the Salt River Valley Water Users' Association, an Arizona
                  corporation, in the case of a transfer by Salt River Project.

            11.4 Except as otherwise provided in Sections 11.1, 11.2 and 11.6
      hereof, any successor to the rights, titles and interests of a Co-Tenant
      in the Navajo Project, together with an equal interest in the Project
      Agreements, shall assume and agree to fully perform and discharge all of
      the obligations hereunder of such Co-Tenant, and such successor shall
      notify each of the other Participants in writing of such transfer,
      assignment or merger, and shall furnish to each Participant evidence of
      such transfer, assignment or merger.

            11.5 No Participant shall be relieved of any of its obligations
      under the Project Agreements by an assignment under this Section 11
      without the express prior written consent of all of the remaining
      Participants.

            11.6 The rights set forth in Sections 11.1, 11.2 and 11.3 hereof
      shall not apply to such interests of Salt River Project in the Navajo
      Project or in the Project Agreements as are held for the use and benefit
      of the United States, and Salt River Project shall transfer,

                                      -31-
<PAGE>

      convey, mortgage, encumber or hypothecate any such interest only upon the
      prior written instruction of the United States.

12.    RIGHT OF FIRST REFUSAL:

            12.1 Except as provided in Section 11 hereof, should any Co-Tenant
      desire to transfer its ownership in the Navajo Project or any part thereof
      to any person, entity or another Co-Tenant, each remaining Co-Tenant shall
       have the right of first refusal to purchase such interest on the basis of
      the greater of the following amounts:

                  12.1.1 The amount of the bona fide written offer from the
                         prospective buyer, or

                   12.1.2 The fair market value.

            12.2 If more than one of the Co-Tenants desire to purchase such
      interest, unless otherwise agreed, it shall be transferred in the ratio
      that the Generation Entitlement Share of each Co-Tenant desiring to
      purchase bears to the total Generation Entitlement Shares of such Co-
      Tenants.

            12.3 At least three (3) years prior to the date on which the
      intended transfer is to be consummated, the Co-Tenant desiring to transfer
      shall serve written notice of its intention to do so upon all of the
      Participants. Such notice shall contain the proposed date of transfer and
      the terms and conditions of the transfer.

                                      -32-
<PAGE>

            12.4 Each Co-Tenant shall have the option to purchase all or any
      part of the interest to be transferred and shall exercise said option by
      serving written notice of its intention upon the Co-Tenant desiring to
      transfer and on the remaining Participants within one hundred eighty (180)
      days after service of the written notice of intention to transfer given
      pursuant to Section 12.3 hereof. Failure by a Co-Tenant to exercise said
      option as provided herein within the time period specified shall be
      conclusively deemed to be an election not to exercise said option.

            12.5 If the Co-Tenants fail to exercise their option to purchase the
      entire ownership interest to be transferred, then the Co-Tenant desiring
      to transfer shall serve written notice of this fact upon the remaining
      Participants within ten (10) days after its receipt of the last of the
      written notices given pursuant to Section 12.4 hereof, or after the
      expiration of the one hundred eighty (180) day period referred to in
      Section 12.4 hereof, whichever is earlier.

            12.6 The Co-Tenants who exercised their option to purchase less than
      the entire ownership interest to be transferred shall have the option to
      purchase the remaining ownership interest to be transferred, which such
      option shall be exercised by serving written notice of such election upon
      the Co-Tenant desiring to transfer

                                      -33-

<PAGE>

      within thirty (30) days after the receipt of the notice given pursuant to
      Section 12.5 hereof.

            12.7 When the options to purchase all or any portion of said
      ownership interest have been exercised, the Co-Tenants shall thereby incur
      the following obligations:

           12.7.1 The Co-Tenant desiring to transfer the ownership interest and
                  the Co-Tenants having exercised the option to purchase all or
                  any portion of such ownership interest shall be obligated to
                  proceed in good faith and with due diligence to obtain all
                  required authorizations and approvals for such purchase.

           12.7.2 The Co-Tenant desiring to transfer such ownership interest
                  shall be obligated to obtain the release of any lien en-
                  cumbering the ownership interest which is the subject of the
                  transfer at the earliest practicable date.

           12.7.3 The Co-Tenants having exercised the option to purchase such
                  ownership interest shall be obligated to perform all of the
                  terms and conditions required of them to complete the purchase
                  of said ownership interest.

                                       -34-
<PAGE>
`
            12.8 The purchase of the ownership interest by the Co-Tenants having
      elected to purchase the same shall be fully consummated within thirty (30)
      months following, the date upon which all notices required to be given
      under this Section 12 have been duly served, unless the Co-Tenants are
      then diligently pursuing applications for required authorizations or
      approvals to effect such transfer or are then diligently pursuing or
      defending appeals from orders entered or authorizations issued in
      connection with such applications, in which event the transfer shall be
      consummated within twelve (12) months following the date upon which the
      final order is entered or authorization issued in connection with such
      applications.

            12.9 If the Co-Tenants fail to exercise their option to purchase all
      of the ownership interest to be transferred, the Co-Tenant desiring to
      transfer such interest shall be free to transfer all, but not less than
      all, of such interest to the party that made the offer to purchase
      referred to in Section 12.1 hereof upon the terms and conditions set forth
      in said bona fide written offer. If such transfer is not consummated by
      the proposed date of transfer referred to in Section 12.3 hereof, the
      Co-Tenant desiring to transfer said ownership interest must give another
      complete new right of first refusal to the remaining Co-Tenants pursuant
      to the

                                      -35-
<PAGE>


      provisions of this Section 12 before such Co-Tenant shall be free to
      transfer said ownership interest to another party.

            12.10 The Co-Tenants who purchase the ownership interest pursuant to
      this Section 12 shall receive title to and shall own the interest as
      tenants in common, subject to the same rights, duties and obligations as
      are applied by the Project Agreements to the interest being transferred in
      the hands of the transferring Co-Tenant.

            12.11 Any Co-Tenant transferring an ownership interest pursuant to
      the provisions of this Section 12 shall remain liable and obligated for
      the performance of all of the terms and conditions of the Project
      Agreements, unless otherwise agreed to by all of the remaining
      Participants.

            12.12 Any party who may succeed to an ownership interest pursuant to
      this Section 12 shall specifically agree in writing with the remaining
      Participants at the time of such transfer that it will not transfer or
      assign all or any portion of such ownership interest without complying
      with the terms and conditions of this Section 12.

            12.13 The provisions of this Section 12 shall not apply to any
      interest held by the Salt River Project for the use and benefit of the
      United States.

13.    DESTRUCTION :

            13.1 If a generating unit of the Navajo Generat-


                                        36


<PAGE>

      ing Station should be destroyed to the extent that the cost of repairs or
      reconstruction is less than 60% of the original cost thereof, the
      Participants shall, unless otherwise agreed, repair or reconstruct such
      generating unit to substantially the same general character or use as the
      original. The Participants shall share the costs of such repair or
      reconstruction in proportion to their Generation Entitlement Shares in the
      generating unit so destroyed.

            13.2 If a generating unit of the Navajo Generating Station should be
      destroyed to the extent that the cost of repairs or reconstruction is 60%
      or more of the original costs thereof, the Participants shall, upon
       agreement, restore or reconstruct, such unit to substantially the same
      general character or use as the original; provided, however, that should
      all of the Participants not agree to restore or reconstruct such unit, but
      some of the Participants nevertheless desire so to do, then the
      Participants who do not agree to restore or reconstruct shall sell their
      interests in such unit to the remaining Participants at a price equal to
      the salvage value of such interests. The Participants agreeing to restore
      or reconstruct such unit shall share the costs of restoration or
      reconstruction in the proportion that the Generation Entitlement Share of
      each bears to the total of Generation Entitlement Shares of such
       Participants.

                                      -37-
<PAGE>

            13.3 If any facilities of the Transmission System, the Railroad or
      the pumping plant should be destroyed, the Participants shall, unless
      otherwise agreed, repair or reconstruct such facilities. The Participants
      shall share the costs of such repair or reconstruction in proportion to
      their cost responsibility for the facilities so destroyed.

14.    SEVERANCE OF IMPROVEMENTS: Except as provided in Section 12 of the
      Indenture of Lease, the Co-Tenants agree that all facilities, structures,
      improvements, equipment and property of whatever kind and nature
      constructed, placed or affixed on the rights-of-way, easements, patented
      and leased lands as part of or as a Capital Improvement to the Navajo
      Project, as against all parties and persons whomsoever (including without
      limitation any party acquiring any interest in the rights-of-way,
      easements, patented or leased lands or any interest in or lien, claim or
      encumbrance against any of such facilities, structures, improvements,
      equipment and property of whatever kind and nature), shall be deemed to be
      and remain personal property of the Co-Tenant(s), not affixed to the
      realty.

15.    CAPITAL IMPROVEMENTS:

            15.1 The Participants recognize that from time to time it may be
      necessary or desirable to make Capital Improvements or that Capital
      Improvements may be required


                                        38




<PAGE>

      by laws and regulations applicable to the Navajo Project.

            15.2 If requested by a Participant, any such Capital Improvement
      shall be described in a supplement to this Co-Tenancy Agreement executed
      in recordable form.

            15.3 The rights, titles and interests, including undivided
      percentage ownership interests, of any Participant in and to any Capital
      Improvements to the Navajo Generating Station shall be held as provided in
      Section 6.1 hereof.

            15.4 Except as specifically provided in Section 6.2.5 hereof,
      Capital Improvements made to the Transmission System shall be owned by the
      Participant(s) in percentage ownership interest(s) in proportions equal to
      their construction cost responsibility (ies) for such Capital
      Improvements; provided, that title to the interest of the United States in
      any such Capital Improvements shall be held by the Salt River Project for
      the use and benefit of the United States.

16.    INTERESTS HELD FOR THE USE AND BENEFIT OF THE UNITED STATES :

            16.1 Salt River Project shall acquire and hold the interests
      acquired for the use and benefit of the United States so that the United
      States will realize the full use and benefit of its entitlement as
      provided for in the Project Agreements.

            16.2 Salt River Project shall not execute any

                                      -39-
<PAGE>

      Project Agreement or any other agreement which purports to apply to the
      rights, titles or interests held for the use and benefit of the United
      States to which the United States is not a contracting party in its
      capacity as a Participant without the prior written consent of the United
      States. Except as otherwise provided in the Project Agreements, Salt River
      Project shall not exercise any rights, privileges or options in any such
      agreement for or on behalf of the United States without the prior written
      consent of the United States. With respect to any Project Agreement to
      which the United States is not a contracting party, except as otherwise
      provided in the Project Agreements, the United States shall have a right,
      co-equal with the rights of the Participants who are contracting parties
      to such Project Agreement, to participate in any decision or action taken
      under such Project Agreement which in any manner applies to or affects a
      right, title or interest held by Salt River Project for the use and
      benefit of the United States, to the same extent and to the same effect as
      though the United States were a contracting party to such Project
      Agreement.

            16.3 Although it is the intention of the Participants that no
      Co-Tenant should incur any additional liability or burden by reason of the
      generating and transmission Capacity dedicated for the use and benefit of
      the United States, should any such liability or burden

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      be imposed upon Salt River Project solely by reason of its holding legal
      title to any portion of the Navajo Project or holding an interest in the
      Project Agreements for the use and benefit of the United States, such
      liability or burden shall be shared by the Co-Tenants and allocated among
      them in the ratio that each Co-Tenant's Generation Entitlement Share bears
      to the total of the Generation Entitlement Shares of the Co-Tenants. To
      the extent any such liability or burden is remedied by money payment,
      performance or otherwise subsequent to its allocation to the Co-Tenants,
      Salt River Project shall reimburse or recompense the Co-Tenants in the
      same ratio as such liability or burden was shared among them.

            16.4 All moneys paid to Salt River Project pursuant to the Project
      Agreements which are for the use and benefit of the United States shall be
      segregated from Salt River Project's general funds and, upon written
      request of the Contracting Officer, such funds will be invested by Salt
      River Project in the manner specified in such request. All interest earned
      and appreciation in value on such investments shall inure to the benefit
      of the United States and all losses on such investments shall be at the
      risk of the United States. If the proceeds exceed the amount of the
      obligation for which they are designated or held, then, upon written
      request of the Contracting Officer, Salt River Project shall pay such

                                      -41-
<PAGE>

      excess to the United States or its designee.

17.    REIMBURSEMENT FOR COSTS AND EXPENSES: The United States shall reimburse
      Salt River Project for all costs and expenses not otherwise specifically
      provided for which are imposed upon, measured by or associated with the
      interests held by Salt River Project for the use and benefit of the United
      States in accordance with the Project Agreements.

18.    DEFAULTS AND COVENANTS REGARDING OTHER AGREEMENTS:

            18.1 Each Participant hereby agrees that it shall pay all monies and
      carry out all other duties and obligations agreed to be paid and/or
      performed by it pursuant to all of the terms and conditions set forth and
      contained in the Project Agreements, and a default by any Participant in
      the covenants and obligations to be kept and performed pursuant to the
      terms and conditions set forth and contained in any of the Project
      Agreements shall be an act of default under this Co-Tenancy Agreement.

            18.2 In the event of a default by any Participant in any of the
      terms and conditions of the Project Agreements, then, within ten (10) days
      after written notice has been given by any non-defaulting Participant to
      all other Participants of the existence and nature of the default, the
      non-defaulting Participants shall remedy such default either by advancing
      the necessary funds

                                      -42-
<PAGE>

      and/or commencing to render the necessary performance, with each
      non-defaulting Participant contributing to such remedy in the ratio of its
      Generation Entitlement Share to the total of the Generation Entitlement
      Shares of all non-defaulting Participants.

            18.3 In the event of a default by any Participant in any of the
      terms and conditions of the Project Agreements and the giving of notice as
      provided in Section 18.2 hereof, the defaulting Participant shall take all
      steps necessary to cure such default as promptly and completely as
      possible and shall pay promptly upon demand to each non-defaulting
      Participant the total amount of money and/or the reasonable equivalent in
      money of non-monetary performance, if any, paid and/or made by such
      non-defaulting Participant in order to cure any default by the defaulting
      Participant, together with interest on such money and/or the costs of
      non-monetary performance at the rate of ten per cent (10%) per annum, or
      the maximum rate of interest legally chargeable, whichever is the lesser,
      from the date of the expenditure of such money and/or the date of
      completion of such non-monetary performance by each such non-defaulting
      Participant to the date of such reimbursement by the defaulting
      Participant, or such greater amount as may be otherwise provided in the
      Project Agreements.

            18.4 In the event that any Participant shall

                                      -43-
<PAGE>

      dispute an asserted default by it, then such Participant shall pay the
      disputed payment or perform the disputed obligation, but may do so under
      protest. The protest shall be in writing, shall accompany the disputed
      payment or precede the performance of the disputed obligation, and shall
      specify the reasons upon which the protest is based. Copies of such
      protest shall be mailed by such Participant to all other Participants.
      Payments not made under protest shall be deemed to be correct, except to
      the extent that periodic or annual audits may reveal over or under
      payments by Participants, necessitating adjustments. In the event it is
      determined by arbitration, pursuant to the provisions of this Co-Tenancy
      Agreement or otherwise, that a protesting Participant is entitled to a
      refund of all or any portion of a disputed payment or payments or is
      entitled to the reasonable equivalent in money of non-monetary performance
      of a disputed obligation theretofore made, then, upon such determination,
      the non-protesting Participants shall pay such amount to the protesting
      Participant, together with interest thereon at the rate of six per cent
      (6%) per annum from the date of payment or from the date of completion of
      performance of a disputed obligation to the date of reimbursement.
      Reimbursement of the amount so paid shall be made by the non-protesting
      Participants in the ratio of their respective Generation Entitlement
      Shares to


                                       44
<PAGE>

      the total of the Generation Entitlement Shares of all non-protesting
      Participants.

            18.5 Unless otherwise determined by a board of arbitrators, in the
      event a default by any Co-Tenant in the payment or performance of any
      obligation under the Project Agreements shall continue for a period of six
      (6) months or more without having been cured by the defaulting Co-Tenant
      or without such Co-Tenant having commenced or continued action in good
      faith to cure such default, or in the event the question of whether an act
      of default exists is the subject of arbitration and such default continues
      for a period of six (6) months following a final determination by a board
      of arbitrators or otherwise that an act of default exists and the
      defaulting Co-Tenant has failed to cure such default or to commence such
      action during said six (6) month period, then, at any time thereafter and
      while said default is continuing, all of the non-defaulting Co-Tenants
      may, by written notice to all Participants, suspend the right of the
      defaulting Co-Tenant to receive all or any part of its proportionate share
      of the Net Effective Generating Capability, in which event:

          18.5.1 During the period that such suspension is in effect, the
                  non-defaulting Participants shall bear all of the operation
                 and maintenance costs, insurance costs and other expenses

                                      -45-
<PAGE>

                 otherwise payable by the defaulting Co-Tenant under the
                 Project Agreements in the ratio of their respective Generation
                 Entitlement Shares to the total of the Generation Entitlement
                 Shares of all non-defaulting Participants.

          18.5.2 A defaulting Co-Tenant shall be liable to the non-defaulting
                 Participants (in the proportion that the Generation
                 Entitlement Share of each non-defaulting Participant bears to
                 the total of the Generation Entitlement Shares of all
                 non-defaulting Participants) for all costs incurred by such
                 non-defaulting Participants pursuant to Section 18.5.1 hereof.
                 The proceeds paid by any defaulting Co-Tenant to remedy any
                  such default shall be distributed to the non-defaulting
                 Participants in the ratio of their respective Generation
                 Entitlement Shares to the total of the Generation Entitlement
                 Shares of all non-defaulting Participants.

            18.6 In addition to the remedies provided for in Section 18.5 of
      this Co-Tenancy Agreement, the non-defaulting Participants may, in
      submitting a dispute to arbitration in accordance with the provisions of
       Section 19 hereof, request that the board of arbitrators determine what
      additional remedies may be reasonably necessary or

                                      -46-
<PAGE>

      required under the circumstances which give rise to the dispute. The board
      of arbitrators may determine what remedies are necessary or required in
      the premises, including but not limited to the conditions under which the
      Navajo Generating Station may be operated economically and efficiently
      during periods when the defaulting Co-Tenant's right to receive its
      proportionate share of the Net Effective Generating Capability is
      suspended.

            18.7 The rights and remedies of the Participants set forth in this
      Co-Tenancy Agreement shall be in addition to the rights and remedies of
      the Participants set forth in any other of the Project Agreements.

            18.8 Notwithstanding the provisions of Sections 18.3 and 18.4
      hereof, the United States shall not pay or be held liable for any interest
      charges, except as otherwise provided in Section 18.9 hereof.

            18.9 In the event a default by the United States in any of its
      obligations to advance funds in accordance with the provisions of the
      Project Agreements is remedied by the non-defaulting Participants as
      provided in Section 18.2 hereof, the United States will reimburse each
      contributing Participant for its costs of money thereby incurred if there
      is in effect at the time of such reimbursement an Act of Congress
      expressly authorizing such reimbursement to be made by the United States.
      For the purposes of this Section 18.9, "costs of money" shall


                                       47
<PAGE>

      mean the contributing Participant's average cost of borrowed capital
      during the period in which its funds are advanced to remedy a default by
      the United States.

19.    ARBITRATION:

            19.1 If a dispute between any of the Participants should arise under
      the Project Agreements which does not involve the legal rights of or which
      will not create a legal obligation upon the United States under the
      Project Agreements, or will not affect the interests or rights held for
      the use and benefit of the United States under the Project Agreements,
      any Participant(s) may call for submission of the dispute to arbitration,
      which call shall be binding upon all of the other Participants.

            19.2 The Participant(s) calling for arbitration shall give written
      notice to all other Participants, setting forth in such notice in adequate
      detail the nature of the dispute, the amount or amounts, if any, involved
      in such dispute, and the remedy sought by such arbitration proceedings,
      and, within twenty (20) days from receipt of such notice, any other
      Participant(s) involved may, by written notice to the first Participant(s)
      and all other Participants, prepare its or their own statement of the
      matter at issue and set forth in adequate detail additional related
      matters or issues to be arbitrated. Thereafter, the Participant(s) first
      submitting its or their statement of the matter at issue shall have ten
      (10)

                                       -48-
<PAGE>

      days in which to submit a rebuttal statement, copies of which shall be
      given to all other Participants.

            19.3 Within ten (10) days following the submission of the rebuttal
      statement, the Participants, acting through their representatives on the
      Coordinating Committee, shall meet for the purpose of selecting
      arbitrators. Each Participant or group of Participants representing one
      side of the dispute shall designate an arbitrator. The arbitrators so
      selected shall meet within twenty (20) days following their selection and
      shall select additional arbitrators, the number of which shall be one (1)
      less than the number of arbitrators selected by the Participants. If the
      arbitrators selected by the Participants, as herein provided, shall fail
      to select such additional arbitrator(s) within said twenty (20) day
      period, then the arbitrators shall request from the American Arbitration
      Association (or a similar organization if the American Arbitration
      Association should not at that time exist) a list of arbitrators who are
      qualified and eligible to serve as hereinafter provided. The arbitrators
      selected by the Participants shall take turns striking names from the list
      of arbitrators furnished by the American Arbitration Association, and the
      last name(s) remaining on said list shall be the additional arbitrator(s).
      All arbitrators shall be persons skilled and experienced in the field
      which gives

                                      -49-
<PAGE>

      rise to the dispute, and no person shall be eligible for appointment as an
      arbitrator who is an officer or employee of any of the parties to the
      dispute or is otherwise interested in the matter to be arbitrated.

            19.4 Except as otherwise provided in this Section 19, the
      arbitration shall be governed by the rules and practice of the American
      Arbitration Association (or the rules and practice of a similar
      organization if the American Arbitration Association should not at that
      time exist) from time to time in force, except that if such rules and
      practice, as modified herein, shall conflict with the Arizona Revised
       Statutes or any other provisions of Arizona law or Federal law, as the
      case may be, then in force which are specifically applicable to
      arbitration proceedings, such law shall govern.

            19.5 Included in the issues which may be


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