EXHIBIT 99.4

CO-LOCATION AGREEMENT

This Co-location Agreement (“Agreement”), dated as of December 8, 2005, by and between Instinet Holdings Incorporated f/k/a Iceland Acquisition Corp., a Delaware corporation (“Newco”), Norway Acquisition Corp. f/k/a Instinet Group Incorporated, a Delaware corporation (“Company”) and The Nasdaq Stock Market, Inc., a Delaware corporation (“Parent”).

WHEREAS, Company entered into that certain Agreement and Plan of Merger, dated as of April 22, 2005, by and among Instinet Group Incorporated, a Delaware corporation (“Iceland”), Parent and Company, pursuant to which, among other things, Company merged with and into Iceland (the “Merger”);

WHEREAS, concurrently therewith, Newco, Company and Parent entered into that certain Transaction Agreement dated as of April 22, 2005 (the “Transaction Agreement”), pursuant to which Parent and Company agreed to sell to Newco all of the Newco Assets;

WHEREAS, the Transaction Agreement provides that Newco and Company shall enter into certain Ancillary Agreements, including this Agreement; and

WHEREAS, pursuant to the Transaction Agreement and in order to ensure an orderly transition of Company following the Merger and sale of the Newco Assets, Newco and Company are entering into this Agreement, pursuant to which Newco will provide or cause to be provided certain co-location services to Company and its Subsidiaries following the Closing Date.

NOW, THEREFORE, in consideration of the Transaction Agreement, the premises and of the mutual covenants, representations, warranties and agreements contained herein and therein, the parties hereto agree as follows:

ARTICLE I

CERTAIN DEFINITIONS

Section 1.01 Capitalized terms used but not defined herein shall have the respective meanings ascribed to them in the Transaction Agreement.

ARTICLE II

LICENSE

Section 2.01 Co-Location Space Use

(a) Co-Location Services . From and after the Closing Date, on the terms and subject to the conditions contained herein and the obtaining by Newco of any necessary consents, Company and its Subsidiaries (collectively, “Services Recipients”) may use,

within the existing data center space designated on Exhibit A (the “Licensed Space”), up to that amount of segregated space and consume up to that amount of power resources designated on Exhibit A for the purpose of hosting computer and communication equipment of Services Recipients and their customers. The Newco resources required to support Services Recipients use of Licensed Space shall be consistent with the resources and intensity of use of those resources provided Services Recipients’ predecessor in the six months before the effective date of the Transaction Agreement (except to the extent any reduction to such resources is not, individually or in the aggregate with all reductions to any services, materially adverse to the conduct of Services Recipients’ business or Services Recipients’ relationship with any customer, and provided such reduction is consistent with a reduction in such resources with respect to Newco’s business).

(b) Common Area Access . From and after the Closing Date, on the terms and subject to the conditions contained herein and the obtaining by Newco of any necessary consents, Services Recipients may enter and use the common areas of the Harborside Financial Center Data Center (the “Building”), including general parking areas (designated for employees), common entrances, common elevators and common bathrooms, in a manner consistent with the access to such common areas Services Recipients predecessor had and the intensity of their use of such common areas before the Closing (except to the extent any reduction to such access is not, individually or in the aggregate with all reductions to any services, materially adverse to the conduct of Services Recipients’ business or Services Recipients’ relationship with any customer, and provided that such reduction is consistent with a reduction in such access with respect to Newco’s business), and subject to such reasonable rules and regulations as exist in connection with such areas as of the Closing Date and any restrictions imposed by the owner or operator of the Building.

(c) Customer Co-location . From and after the Closing Date, on the terms and subject to the conditions contained herein and the obtaining by Newco of any necessary consents, Services Recipients are permitted to allow their customers to co-locate with the Licensed Space or common areas provided that (i) such co-location is consistent with any restrictions imposed by the owner or operator of the Building; (ii) with each new co-located customer following the Closing, Services Recipients shall enter into a written agreement that incorporates the conditions and restrictions set forth herein with respect to use of the Licensed Space; and (iii) any amendment to any Existing Co-Location Agreement (as defined below) shall incorporate the conditions and restrictions set forth herein with respect to use of the Licensed Space.

(d) Telecommunications . At the request of the Services Recipients and subject to obtaining any necessary consents, Newco will take necessary steps, at Company’s cost and expense, to transfer telecommunications contracts for lease lines relating solely to the Services Recipients’ business and will take reasonable steps to allow the Services Recipients to continue to use shared circuits if needed to conduct business in a pre-Closing manner with Services Recipients bearing half the costs of any such shared circuits.

Section 2.02 Services . In addition, Newco shall provide from time to time upon the request of Services Recipients the support services set forth in Exhibit A (the “Support Services” and, together with the provision of the Licensed Space, the “Services”). The Support

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Services will be provided in all respects with the same frequency, performance capability, functionality, capacity and accuracy as such services were provided by Iceland during the six (6) month period prior to the Closing (except to the extent any reduction in the frequency, performance capability, functionality, capacity and accuracy of such services is not, individually or in the aggregate with all reductions to any services, materially adverse to the conduct of Services Recipients’ business or Services Recipients’ relationship with any customer, and provided that such reduction is consistent with a reduction in the frequency, performance capability, functionality, capacity and accuracy of such services with respect to Newco’s business), provided that the Services shall be provided at all times (a) to Services Recipients in accordance with applicable law; and (b) to Services Recipients’ co-located customers that are parties to a co-location agreement set forth on Exhibit B (collectively, the “Existing Co-location Agreements”), in accordance with the terms of the respective Existing Co-location Agreement.

Section 2.03 Equipment Installation and Removal . Prior to the end of the Term, Services Recipients shall remove from the Licensed Space all of their property and the property of their customers, and shall repair any damage to the Licensed Space or the Building resulting from the installation, use or removal of such property.

Section 2.04 Condition of Licensed Space . Services Recipients hereby acknowledge that they have inspected the Licensed Space and agree to accept same in its “as is” condition as of the Closing Date, provided that Newco agrees to maintain the Licensed Space in such condition for the Term. Company further acknowledges and agrees that the Services Recipients, co-located customers and their employees and other representatives shall use due care in their use of the Licensed Space and any common areas, the fixtures and other existing structures in such locations.

Section 2.05 Alterations . Services Recipients, at their expense, shall have the right to make installations, repairs, alterations, improvements, changes, decorations or additions in or to the Licensed Space, provided that Services Recipients will not make any alterations that (i) are structural in nature; (ii) affect the exterior of any structural portions or components of the Building; or (iii) negatively affect Newco, any of its co-located customers, or any equipment of Newco or its co-located customers.

Section 2.06 TCP/IP Addresses . Upon termination or expiration of this Agreement for any reason, Newco, at the cost and expense of Services Recipients, shall take all steps and execute all documents to transfer all registered TCP/IP addresses used by Services Recipients or their customers to the Company or its designee(s).

Section 2.07 Service Coordinators; Dispute Resolution

(a) Newco and Company shall each nominate a representative to act as the primary contact person with respect to the performance of the Services (each, a “Service Coordinator”). Unless otherwise agreed by the parties, all communications relating to this Agreement and to the Services provided hereunder shall be directed to the Service Coordinators. The initial Service Coordinators for