AMENDMENT TO MASTER TRUST AGREEMENT

Exhibit 10.48

AMENDMENT TO

MASTER TRUST AGREEMENT

THIS AMENDMENT to the Master Trust Agreement (the “Amendment”) is entered into as of January 1, 2006, between DYNEGY INC., an Illinois corporation (the “Employer”) and VANGUARD FIDUCIARY TRUST COMPANY, a trust company incorporated under Chapter 10 of the Pennsylvania Banking Code (the “Master Trustee”).

WITNESSETH

WHEREAS, the Employer and the Dynegy Inc. Benefit Plans Committee (the “Plan Administrator”) have entered into an agreement (the “FCI Agreement”) with Fiduciary Counselors Inc. (the “Independent Fiduciary”) pursuant to which the Independent Fiduciary was appointed by the Plan Administrator to have the sole and exclusive fiduciary responsibility with respect to the continued offering and operation of the Dynegy Stock Fund and with respect to the continued holding of Class A common stock of the Employer (“Company Stock”) in the Participating Plans (as defined in the Master Trust Agreement);

WHEREAS, pursuant to the FCI Agreement, the Independent Fiduciary received certain powers to direct the Master Trustee with respect to the Dynegy Stock Fund and the Company Stock, and the Independent Fiduciary agreed to perform certain duties with respect to the Dynegy Stock Fund and the Company Stock; and

WHEREAS, the Employer and the Master Trustee deem it necessary and desirable to amend the Master Trust Agreement to reflect the appointment of the Independent Fiduciary and to authorize it to have certain powers and to perform the duties specified in this Amendment with respect to the Dynegy Stock Fund and the Company Stock.

NOW, THEREFORE, in consideration of the mutual covenants herein contained, the parties hereto, intending to be legally bound, hereby agree and declare as follows:

1. The third sentence of Section 1.3 of the Master Trust is hereby amended in its entirety to provide as follows:

“The Plan Administrator may also direct the Master Trustee to deliver assets of this Fund to any of the trust agreements under the Participating Plans.”

2. Section 2.1 of the Master Trust is hereby amended in its entirety to provide as follows:

“The Plan Administrator shall have the exclusive authority and discretion to select the investment funds available for investment under the Participating Plans, other than the Dynegy Stock Fund, which shall be offered as an investment fund available for investment under the Participating Plans in accordance with the provisions of the Participating Plans and Section 2.4 hereof (the selected investment funds and the

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Dynegy Stock Fund are collectively referred to as the “Investment Funds”). The Plan Administrator shall notify the Trustee in writing of the selection of the Investment Funds currently available for investment under the Participating Plans, and any changes thereto. The purpose of the Master Trust is to facilitate the investment of the assets of the Participating Plans.”

3. Subsection 2.2(a) of the Master Trust is hereby amended by adding the phrase, “subject to the provisions of Section 2.4,” to the beginning thereof.

4. Subsection 2.2(b) of the Master Trust is hereby amended in its entirety to provide as follows:

“(b) to dispose of all or any part of the investments, securities other than Company Stock, or other property which may from time to time or at any time constitute the Fund or portion thereof in accordance with the directions by the Plan Administrator furnished to it pursuant to Section 1.3, or to dispose of all or any part of the Company Stock which may from time to time or at any time constitute a portion of the Fund in accordance with the directions by the Independent Fiduciary pursuant to Section 2.4, and to make, execute and deliver to the purchasers thereof good and sufficient deeds of conveyance therefore, and all assignments, transfers and other legal instruments, either necessary or convenient for passing the title and ownership thereto, free and discharged of all trusts and without liability on the part of such purchasers to see to the application of the purchase money;”

5. A new Section 2.4 is hereby added to the Master Trust to provide as follows:

“Section 2.4. Notwithstanding any other provision of this Agreement to the contrary, the Independent Fiduciary shall have the sole and exclusive authority to determine whether acquiring or holding Company Stock in the Participating Plans and Master Trust is no longer consistent with the Employee Retirement Income Security Act of 1974, as amended (“ERISA”), and it shall be the sole named fiduciary for such purpose. If the Independent Fiduciary makes such a determination, it shall have the power to determine whether to:

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The Independent Fiduciary shall direct the Master Trustee to take such actions as are necessary and appropriate to implement and administer the Independent Fiduciary’s determinations under this Section 2.4, and the Master Trustee shall be fully entitled to rely on such directions, and the Master Trustee shall be under no duty to ascertain whether such directions are in accordance with the provisions of the Participating Plans.”

6. Section 3.1 of the Master Trust is hereby deleted and the remaining Sections of Article III renumbered accordingly.

7. The second sentence of Section 4.5 of the Master Trust is hereby amended in its entirety to provide as follows:

“The Master Trustee shall be the fiduciary who is responsible for ensuring that such procedures are sufficient to safeguard the confidentiality of the information described above and that such procedures are followed; provided, however, the Independent Fiduciary shall be the fiduciary responsible for ensuring the confidentiality of the proxy voting process.”

8. A new Section 4.6 is hereby added to the Master Trust to provide as follows:

“Section 4.6. The Independent Fiduciary shall direct the Master Trustee to execute and deliver such forms and other documents as the Independent Fiduciary may determine are advisable to be filed with the Securities and Exchange Commission or other governmental agency, and the Master Trustee shall be fully entitled to rely on such directions.”

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9. Sections 6.1 and 6.2 of the Master Trust are hereby amended by adding the phrase “or the Independent Fiduciary” immediately following the term “Plan Administrator” in such Sections.

10. This Amendment may be executed in separate counterparts, which together shall constitute one agreement.

IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of the day and year first written above.

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