Underwriting Agreement

20,000,000 SHARES

CALPINE CORPORATION

CALPINE CORPORATION COMMON STOCK, $.001 PAR VALUE

UNDERWRITING AGREEMENT

September 22, 2009

Morgan Stanley & Co. Incorporated

Ladies and Gentlemen:

The shareholders named in Schedule I hereto (collectively, the “ Selling Shareholder ”) of Calpine Corporation, a Delaware corporation (the “ Company ”) proposes to sell to Morgan Stanley & Co. Incorporated (the “ Underwriter ” or “ you ”) an aggregate of 20,000,000 shares of Calpine Corporation Common Stock, Par Value $.001 (the “ Firm Shares ”).

The Selling Shareholder also proposes to sell to the Underwriter not more than an additional 3,000,000 shares of Calpine Corporation Common Stock, Par Value $.001 (the “ Additional Shares ”) if and to the extent that the Underwriter shall have determined to exercise the right to purchase such Additional Shares in accordance with Section 3 hereof.  The Firm Shares and the Additional Shares are hereinafter collectively referred to as the “ Shares .” The shares of Calpine Corporation Common Stock, Par Value $.001 of the Company to be outstanding after giving effect to the sales contemplated hereby are hereinafter referred to as the “ Common Stock .” The Company and the Selling Shareholder are hereinafter sometimes collectively referred to as the “ Sellers .”

The Company has filed with the Securities and Exchange Commission (the “ Commission ”) a registration statement (File No. 333-152982), including a prospectus, relating to the Shares.  The registration statement as amended at the time it became effective, including the information (if any) deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A under the Securities Act of 1933, as amended (the “ Securities Act ”), is hereinafter referred to as the “ Registration Statement ”; the prospectus in the form first used to confirm sales of Shares (or in the form first made available to the Underwriter by the Company to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “ Prospectus. ”  If the Company has filed an abbreviated registration statement to register additional shares of Common Stock pursuant to Rule 462(b) under the Securities Act (the “ Rule 462 Registration Statement ”), then any reference herein to the term “ Registration Statement ” shall be deemed to include such Rule 462 Registration Statement.

For purposes of this Agreement, “ free writing prospectus ” has the meaning set forth in Rule 405 under the Securities Act, “ Time of Sale Prospectus ” means the preliminary prospectus together with the free writing prospectuses, if any, each identified in Schedule II hereto, and “ broadly available

road show ” means a “bona fide electronic road show” as defined in Rule 433(h)(5) under the Securities Act that has been made available without restriction to any person.  As used herein, the terms “Registration Statement,” “preliminary prospectus,” “Time of Sale Prospectus” and “Prospectus” shall include the documents, if any, incorporated by reference therein.  The terms “ supplement, ” “ amendment ” and “ amend ” as used herein with respect to the Registration Statement, the Prospectus, the Time of Sale Prospectus or any free writing prospectus shall include all documents subsequently filed by the Company with the Commission pursuant to the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”), that are deemed to be incorporated by reference therein.

1.       Representations and Warranties of the Company .  The Company represents and warrants to and agrees with the Underwriter that:

(a)      The Registration Statement has become effective; no stop order suspending the effectiveness of the Registration Statement is in effect, and no proceedings for such purpose are pending before or threatened by the Commission.  If the Registration Statement is an automatic shelf registration statement as defined in Rule 405 under the Securities Act, the Company is a well-known seasoned issuer (as defined in Rule 405 under the Securities Act) eligible to use the Registration Statement as an automatic shelf registration statement and the Company has not received notice that the Commission objects to the use of the Registration Statement as an automatic shelf registration statement.

(b)      (i) Each document, if any, filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Time of Sale Prospectus or the Prospectus complied or will comply when so filed in all material respects with the Exchange Act and the applicable rules and regulations of the Commission thereunder, (ii) the Registration Statement, when it became effective, did not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (iii) the Registration Statement and the Prospectus comply and, as amended or supplemented, if applicable, will comply in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder, (iv) the Time of Sale Prospectus does not, and at the time of each sale of the Shares in connection with the offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date (as defined in Section  5), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, (v) each broadly available road show, if any, when considered together with the Time of Sale Prospectus, does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and (vi) the

Prospectus does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except that the representations and warranties set forth in this paragraph do not apply to statements or omissions in the Registration Statement, the Time of Sale Prospectus or the Prospectus based upon information relating to any Underwriter furnished to the Company in writing by such Underwriter through you expressly for use therein.

(c)      The Company is not an “ineligible issuer” in connection with the offering pursuant to Rules 164, 405 and 433 under the Securities Act.  Any free writing prospectus that the Company is required to file pursuant to Rule 433(d) under the Securities Act has been, or will be, filed with the Commission in accordance with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder.  Each free writing prospectus that the Company has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act or that was prepared by or behalf of or used or referred to by the Company complies or will comply in all material respects with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder.  Except for the free writing prospectuses, if any, identified in Schedule II hereto, and electronic road shows, if any, each furnished to you before first use, the Company has not prepared, used or referred to, and will not, without your prior consent, prepare, use or refer to, any free writing prospectus.

(d)      The Company has been duly incorporated, is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(e)      Each subsidiary of the Company has been duly incorporated, is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so duly incorporated (other than with respect to any of the Company’s “significant subsidiaries” within the meaning of Rule 1-02 of Regulation S-X), qualified or be in good standing would not have a material adverse effect on the Company and its subsidiaries, taken as a whole; all of the issued shares of capital stock of each subsidiary of the Company have been duly and validly authorized and issued, are fully paid and non-assessable and, except as set forth in the Time of Sale

Prospectus and the Prospectus, are owned directly by the Company, free and clear of all liens, encumbrances, equities or claims.

(f)      This Agreement has been duly authorized, executed and delivered by the Company.

(g)      The authorized capital stock of the Company conforms as to legal matters in all material respects to the description thereof contained in each of the Time of Sale Prospectus and the Prospectus.

(h)      The shares of Common Stock (including the Shares to be sold by the Selling Shareholder) have been duly authorized and, except as set forth in the Time of Sale Prospectus and the Prospectus, are validly issued, fully paid and non-assessable.

(i)      The execution and delivery by the Company of, and the performance by the Company of its obligations under, this Agreement will not contravene any provision of applicable law or the certificate of incorporation or by-laws of the Company or any agreement or other instrument binding upon the Company or any of its subsidiaries that is material to the Company and its subsidiaries, taken as a whole, or any judgment, order or decree of any governmental body, agency or court having jurisdiction over the Company or any subsidiary, and no consent, approval, authorization or order of, or qualification with, any governmental body or agency is required for the performance by the Company of its obligations under this Agreement, except such as may be required by the securities or Blue Sky laws of the various states in connection with the offer and sale of the Shares.

(j)      There has not occurred any material adverse change, or any development involving a prospective material adverse change, in the condition, financial or otherwise, or in the earnings, business or operations of the Company and its subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus.

(k)      There are no legal or governmental proceedings pending or threatened to which the Company or any of its subsidiaries is a party or to which any of the properties of the Company or any of its subsidiaries is subject (i) other than proceedings accurately described in all material respects in the Time of Sale Prospectus and proceedings that would not have a material adverse effect on the Company and its subsidiaries, taken as a whole, or on the power or ability of the Company to perform its obligations under this Agreement or to consummate the transactions contemplated by the Time of Sale Prospectus or (ii) that are required to be described in the Registration Statement or the Prospectus and are not so described; and there are no statutes, regulations, contracts or other documents that are required to be described in the Registration Statement or the Prospectus or to be filed as exhibits to the Registration Statement that are not described or filed as required.

(l)       Each preliminary prospectus filed as part of the registration statement as originally filed or as part of any amendment thereto, or filed pursuant to Rule 424 under the Securities Act, complied when so filed in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder.

(m)     The Company is not, and after giving effect to the sale of the Shares as described in the Prospectus will not be, required to register as an “investment company” as such term is defined in the Investment Company Act of 1940, as amended.

(n)      The Company and its subsidiaries (i) are in compliance with any and all applicable foreign, federal, state and local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (“ Environmental Laws ”), (ii) have received all permits, licenses or other approvals required of them under applicable Environmental Laws to conduct their respective businesses and (iii) are in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not, singly or in the aggregate, have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(o)      There are no costs or liabilities associated with Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up, closure of properties or compliance with Environmental Laws or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties) which would, singly or in the aggregate, have a material adverse effect on the Company and its subsidiaries, taken as a whole.

(p)      There are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Securities Act with respect to any securities of the Company or to require the Company to include such securities with the Shares registered pursuant to the Registration Statement, except pursuant to that certain Registration Rights Agreement made as of January 31, 2008, by and among the Company, the Selling Shareholder and the other parties named therein (which is incorporated by reference as an exhibit to the Registration Statement) (the “ Registration Rights Agreement ”).

(q)      Neither the Company nor any of its subsidiaries, nor any director, officer, or employee, nor, to the Company’s knowledge, any agent or representative of the Company or of any of its subsidiaries or affiliates, has taken or will take any action in furtherance of an offer, payment, promise to pay, or authorization or approval of the payment or giving of money, property, gifts or anything else of value, directly or indirectly, to any “government official”

(including any officer or employee of a government or government-owned or controlled entity or of a public international organization, or any person acting in an official capacity for or on behalf of any of the foregoing, or any political party or party official or candidate for political office) to influence official action or secure an improper advantage; and the Company and its subsidiaries and affiliates have conducted their businesses in compliance with applicable anti-corruption laws and have instituted and maintain and will continue to maintain policies and procedures designed to promote and achieve compliance with such laws and with the representation and warranty contained herein.

(r)      The operations of the Company and its subsidiaries are and have been conducted at all times in material compliance with all applicable financial recordkeeping and reporting requirements, including those of the Bank Secrecy Act, as amended by Title III of the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001 (USA PATRIOT Act), and the applicable anti-money laundering statutes of jurisdictions where the Company and its subsidiaries conduct business, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “ Anti-Money Laundering Laws ”), and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or any of its subsidiaries with respect to the Anti-Money Laundering Laws is pending or, to the best knowledge of the Company, threatened.

(s)      (i)  The Company represents that neither the Company nor any of its subsidiaries (collectively, the “ Entity ”) or , to the knowledge of the Entity, any director, officer, employee, agent or representative of the Entity, is an individual or entity (“ Person ”) that is, or is owned or controlled by a Person that is:

(ii)  The Entity represents and covenants that it will not, directly or indirectly, lend, contribute or otherwise make available any proceeds to any subsidiary, joint venture partner or other Person:

(iii)  The Entity represents and covenants that for the past 5 years, it has not knowingly engaged in, is not now knowingly engaged in, and will not engage in, any dealings or transactions with any Person, or in any country or territory, that at the time of the dealing or transaction is or was the subject of Sanctions.

2.       Representations and Warranties of the Selling Shareholder . Each Selling Shareholder represents and warrants to and agrees with the Underwriter that:

(a)      This Agreement has been duly authorized, executed and delivered by or on behalf of such Selling Shareholder.

(b)      The execution and delivery by such Selling Shareholder of, and the performance by such Selling Shareholder of its obligations under, this Agreement, will not contravene any provision of applicable law, or the certificate of incorporation or by-laws of such Selling Shareholder (if such Selling Shareholder is a corporation), or any agreement or other instrument binding upon such Selling Shareholder or any judgment, order or decree of any governmental body, agency or court having jurisdiction over such Selling Shareholder, and no consent, approval, authorization or order of, or qualification with, any governmental body or agency is required for the performance by such Selling Shareholder of its obligations under this Agreement, except such as may be required by the securities or Blue Sky laws of the various states in connection with the offer and sale of the Shares.

(c)      Such Selling Shareholder has, and on the Closing Date will have, valid title to, or a valid “security entitlement” within the meaning of Section 8-501 of the New York Uniform Commercial Code in respect of, the Shares to be sold by such Selling Shareholder free and clear of all security interests, claims, liens, equities or other encumbrances and the legal right and power, and all authorization and approval required by law, to enter into this Agreement and to sell, transfer and deliver the Shares to be sold by such Selling Shareholder or a security entitlement in respect of such Shares.

(d)      Upon payment for the Shares to be sold by such Selling  Shareholder pursuant to this Agreement, delivery of such Shares, as directed by the Underwriter, to Cede & Co. (“ Cede ”) or such other nominee as may be designated by the Depository Trust Company (“ DTC ”), registration of such Shares in the name of Cede or such other nominee and the crediting of such Shares on the books of DTC to securities account of the Underwriter (assuming that neither DTC nor the Underwriter has notice of any adverse claim (within the meaning of Section 8-105 of the New York Uniform Commercial Code (the “ UCC ”)) to such Shares), (A) DTC shall be a “protected purchaser” of such

Shares within the meaning of Section 8-303 of the UCC, (B) under Section 8-501 of the UCC, the Underwriter will acquire a valid security entitlement in respect of such Shares and (C) no action based on any “adverse claim”, within the meaning of Section 8-102 of the UCC, to such Shares may be asserted against the Underwriter with respect to such security entitlement; for purposes of this representation, the Selling Shareholder may assume that when such payment, delivery and crediting occur, (x) such Shares will have been registered in the name of Cede or another nominee designated by DTC, in each case on the Company’s share registry in accordance with its certificate of incorporation, bylaws and applicable law, (y) DTC will be registered as a “clearing corporation” within the meaning of Section 8-102 of the UCC and (z) appropriate entries to the account of the Underwriter on the records of DTC will have been made pursuant to the UCC.

(d)      The Selling Shareholder has reviewed and is familiar with the Registration Statement, the Time of Sale Prospectus and the Prospectus (at the Closing Date in the case of the Prospectus) and, with respect solely to information provided in writing by the Selling Shareholder that is included therein, has no knowledge of any material fact, condition or information not disclosed in the Time of Sale Prospectus or the Prospectus (at the Closing Date in the case of the Prospectus) that has had, or may have, a material adverse effect on the Company and its subsidiaries, taken as a whole.  The Selling Shareholder is not prompted by any information concerning the Company or its subsidiaries which is not set forth in the Time of Sale Prospectus to sell its Shares pursuant to this Agreement.

(e)      (i) The Registration Statement, when it became effective, did not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (ii) the Registration Statement and the Prospectus comply and, as amended or supplemented, if applicable, will comply in all material respects with the Securities Act and the applicable rules and regulations of the Commission thereunder, (iii) the Time of Sale Prospectus does not, and at the time of each sale of the Shares in connection with the offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date (as defined in Section  5), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, (iv) each broadly available road show, if any, when considered together with the Time of Sale Prospectus, does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and (v) the Prospectus does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except that the representations and

warranties set forth in this paragraph 2(e) shall only apply to statements or omissions in the Registration Statement or the Prospectus based upon information relating to any the Selling Shareholder furnished by or on behalf of the Selling Shareholder in writing expressly for use therein.

3.       Agreements to Sell and Purchase . The Selling Shareholder hereby agrees to sell to the Underwriter, and the Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $11.40 a share (the “ Purchase Price ”) the Firm Shares (subject to such adjustments to eliminate fractional shares as you may determine).

On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, the Selling Shareholder agrees to sell to the Underwriter the Additional Shares, and the Underwriter shall have the right to purchase up to 3,000,000 Additional Shares at the Purchase Price, provided, however, that the amount paid by the Underwriter for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the Company and payable on the Firm Shares but not payable on such Additional Shares.  You may exercise this right on behalf of the Underwriter in whole or from time to time in part by giving written notice not later than 30 days after the date of this Agreement.  Any exercise notice shall specify the number of Additional Shares to be purchased by the Underwriter and the date on which such shares are to be purchased.  Each purchase date must be at least one business day after the written notice is given and may not be earlier than the closing date for the Firm Shares nor later than ten business days after the date of such notice.  Each day, if any, that Additional Shares are to be purchased shall be referred to as an “ Option Closing Date ”.

The Selling Shareholder hereby agrees that, without the prior written consent of the Underwriter it will not, during the period ending 60 days after the date of the Prospectus, (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock; or (2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise; or (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock; provided, however , in the case of clause (1) above, any pledge by t