Exhibit 10.1

February 10, 2010

Allegheny Energy Supply Company, LLC

800 Cabin Hill Drive

Greensburg, PA 15601

Ladies and Gentlemen:

Reference is made to that certain Credit Agreement, dated as of September 24, 2009 (as amended, restated, supplemented or otherwise modified from time to time, the “Credit Agreement”), by and among Allegheny Energy Supply Company, LLC, each of the Initial Lender Parties referred to therein, Bank of America, N.A., as Administrative Agent, and the other parties thereto. Capitalized terms used herein but not defined herein have the respective meanings set forth in the Credit Agreement.

The Borrower and the Required Lenders hereby agree that, as of the date first written above, the Credit Agreement is amended such that clause (d) of the definition of Change of Control appearing alphabetically in Section 1.01 thereof is amended and restated in its entirety as set forth below:

“(d) ninety (90) days shall have elapsed after any Person or two or more Persons acting in concert shall have acquired by contract or otherwise, or shall have entered into a contract or arrangement that, upon consummation, will result in its or their acquisition of the power to exercise, directly or indirectly, a controlling influence over the management or policies of the Parent”.

On and after the effectiveness of this letter agreement, each reference in the Credit Agreement to “this Agreement”, “hereunder”, “hereof” or words of like import referring to the Credit Agreement, and each reference in each of the other Financing Documents to “the Credit Agreement”, “thereunder”, “thereof” or words of like import referring to the Credit Agreement, shall mean and be a reference to the Credit Agreement, as amended by this letter agreement. The Credit Agreement, as specifically amended by this letter agreement, and each of the other Financing Document, is and shall continue to be in full force and effect and is hereby in all respects ratified and confirmed.

The execution, delivery and effectiveness of this Amendment shall not, except as expressly provided herein, operate as an amendment of any right, power or remedy of any Lender Party or the Administrative Agent under any of the Financing Documents, nor constitute a waiver of any provision of any of the Financing Documents.

This letter agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

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Please evidence your agreement to the foregoing by signing and returning a counterpart of this amendment letter to the Administrative Agent.