ex5-1.htm

	Skadden, Arps, Slate, Meagher & Flom llp
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				WASHINGTON, D.C. WILMINGTON
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August 12, 2008				BEIJING BRUSSELS
				FRANKFURT HONG KONG
Calpine Corporation 717 Texas Avenue				LONDON MOSCOW
Houston, Texas 77002				MUNICH PARIS
				SHANGHAI SINGAPORE
		Re: Calpine Corporation Registration Statement on Form S-3		SYDNEY TOKYO
				TORONTO VIENNA

Ladies and Gentlemen:

We have acted as special counsel to Calpine Corporation, a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-3 (the “Registration Statement”), to be filed by the Company with the Securities and Exchange Commission (the “Commission”) on the date hereof under the Securities Act of 1933, as amended (the “Act”). The Registration Statement relates to the sale from time to time by certain selling stockholders (the “Selling Stockholders”) of up to an aggregate of 166,924,198 shares of common stock, par value $0.001 per share, of the Company (the “Common Stock”), including 165,715,835 shares of common stock (the “Common Shares”) presently outstanding and 1,208,363 shares of common stock (the “Warrant Shares”) issuable upon the exercise of outstanding warrants (the “Warrants”). The Common Shares and the Warrant Shares are collectively referred to herein as the “Shares.”

This opinion is being furnished to you in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Act.

In rendering the opinions set forth herein, we have examined and relied on originals or copies, certified or otherwise identified to our satisfaction, of (a) the Registration Statement in the form it is to be filed with the Commission on the date hereof, (b) a specimen certificate evidencing the Common Stock, (c) the Series A Warrant Agreement, dated February 15, 2008, among the Company, Computershare Inc. and Computershare Trust Company, N.A., as warrant agent (the

“Warrant Agreement”), including the form of Warrants issued under the Warrant Agreement, (d) the Company’s Sixth Amended Joint Plan of Reorganization Pursuant to Chapter 11 of the United States Bankruptcy Code, dated December 19, 2007, (e) the Findings of Fact, Conclusions of Law, and Order Confirming Sixth Amended Joint Plan of Reorganization Pursuant to Chapter 11 of the Bankruptcy Code, dated December 19, 2007, (f) the Amended and Restated Certificate of Incorporation of the Company, as amended to the date hereof and as certified by the Secretary of State of the State of Delaware, (g) the Amended and Restated Bylaws of the Company, as currently in effect, and (h) certain resolutions of the Board of Directors of the Company.

We have also examined originals or copies, certified or otherwise identified to our satisfaction, of such records of the Company and such agreements, certificates of public officials, certificates of officers or other representatives of the Company and others, and such other documents, certificates and records as we have deemed necessary or appropriate as a basis for the opinions set forth herein.

In our examination, we have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as facsimile, electronic, certified or photostatic copies, and the authenticity of the originals of such copies. In making our examination of executed documents, we have assumed that the parties thereto, other than the Company, had the power, corporate or other, to enter into and perform all obligations thereunder and have also assumed the due authorization by all requisite action, corporate or other and the execution and delivery by such parties of such documents and the validity and binding effect thereof on such parties. In rendering the opinion set forth in paragraph 1 below, we have assumed that (i) the Company has received the entire amount of the consideration contemplated by the resolutions of the Board of Directors of the Company authorizing the issuance of the Common Shares; (ii) that the registrar and transfer agent for the Common Stock duly registered the issuance of the Common Shares and countersigned the stock certificates evidencing such Common Shares; and (iii) that such stock certificates conform to the specimen certificate examined by us. In rendering the opinion set forth in paragraph 2 below, we have assumed that (i) the Warrant Shares will be issued upon the exercise of the Warrants in accordance with the terms of the Warrants; (ii) the registrar and transfer agent for the Common Stock will duly register such issuance and countersign the stock certificates evidencing such Warrant Shares; and (iii) such stock certificates will conform to the specimen certificate examined by us. As to any facts material to the opinions expressed herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Company and others and of public officials.

Members of our firm are admitted to the bar in the State of New York, and we do not express any opinion as to the laws of any other jurisdiction other than

the corporate laws of the State of Delaware, and we do not express any opinion as to the effect of any other laws on the opinions stated herein. The Shares may be offered and sold by the Selling Stockholders from time to time on a delayed or continuous basis, and this opinion is limited to the laws as in effect on the date hereof, which laws are subject to change with possible retroactive effect.

Based upon and subject to the foregoing, we are of the opinion that:

1. The Common Shares have been duly authorized and validly issued and are fully paid and nonassessable.

2. The Warrant Shares have been duly authorized and, when issued upon exercise of the Warrants and paid for in accordance with the terms of the Warrants, will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion with the Commission as an exhibit to the Registration Statement. We also consent to the reference to our firm under the caption “Legal Matters” in the Registration Statement. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission. This opinion is expressed as of the date hereof unless otherwise expressly stated, and we disclaim any undertaking to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable laws.

Very truly yours,

/s/ Skadden, Arps, Slate, Meagher & Flom LLP