EX-5.1

We have acted as your special United States counsel in connection with the above-referenced Registration Statement on Form F-4 (the “Registration Statement”) filed on the date hereof by Petróleos Mexicanos (the “Issuer”) and Pemex Exploración y Producción, Pemex-Refinación, Pemex-Gas y Petroquímica Básica and Pemex Cogeneración y Servicios (the “Guarantors”), with the United States Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Act”), in connection with the proposed offers to exchange (the “Exchange Offers”) up to U.S. $1,500,000,000 aggregate principal amount of 3.500% Notes due 2020 (the “2020 New Notes”), U.S. $1,000,000,000 aggregate principal amount of 4.250% Notes due 2025 (the “2025 New Notes”), U.S. $1,500,000,000 aggregate principal amount of 4.500% Notes due 2026 (the “2026 New Notes”), U.S. $1,500,000,000 aggregate principal amount of 5.50% Bonds due 2044 (the “2044 New Bonds”) and U.S. $3,000,000,000 aggregate principal amount of 5.625% Bonds due 2046 (the “2046 New Bonds” and, together with the 2020 New Notes, the 2025 New Notes, the 2026 New Notes and the 2044 New Bonds, the “New Securities”) that have been registered under the Act for an equal principal amount of the Issuer’s issued and outstanding 3.500% Notes due 2020 (the “2020 Old Notes”), 4.250% Notes due 2025 (the “2025 Old Notes”), of 4.500% Notes due

2026 (the “2026 Old Notes”), 5.50% Bonds due 2044 (the “2044 Old Bonds”) and 5.625% Bonds due 2046 (the “2046 Old Bonds” and, together with the 2020 Old Notes, the 2025 Old Notes, the 2026 Old Notes and the 2044 Old Bonds, the “Old Securities”). The New Securities will be issued pursuant to an indenture dated as of January 27, 2009, between the Issuer and Deutsche Bank Trust Company Americas, as trustee (the “Trustee”), as supplemented by (i) the First Supplemental Indenture, dated as of June 2, 2009, among the Issuer, the Trustee and Deutsche Bank AG, London Branch as International Paying Agent, (ii) the Second Supplemental Indenture, dated as of October 13, 2009, among the Issuer, the Trustee, Credit Suisse, as Principal Swiss Paying Agent and Authenticating Agent, and BNP Paribas (Suisse) SA, as Swiss Paying Agent, (iii) the Third Supplemental Indenture, dated as of April 10, 2012, among the Issuer, the Trustee and Credit Suisse AG, as Swiss Paying Agent and Authenticating Agent, (iv) the Fourth Supplemental Indenture, dated as of June 24, 2014, between the Issuer and the Trustee and (v) the Fifth Supplemental Indenture, dated as of October 15, 2014, between the Issuer and the Trustee (as supplemented, the “Indenture”). Pursuant to a guaranty agreement dated July 29, 1996 (the “Guaranty Agreement”) among the Issuer and the Guarantors, and certificates of designation dated October 15, 2014 and January 23, 2015 (the “Certificates of Designation”) issued by the Issuer thereunder, all of the Issuer’s payment obligations under the New Securities will be unconditionally guaranteed, jointly and severally, by the Guarantors.

In arriving at the opinions expressed below, we have reviewed the following documents:

In addition, we have made such investigations of law, as we have deemed appropriate as a basis for the opinion expressed below.

In rendering the opinions expressed below, we have assumed the authenticity of all documents submitted to us as originals and the conformity to the originals of all documents submitted to us as copies. In addition, we have assumed and have not verified (i) the accuracy as to factual matters of each document we have reviewed, (ii) that the New Securities will conform to the forms thereof that we have reviewed and will be duly authenticated in accordance with the Indenture, (iii) that Pemex Exploración y Producción and Pemex Cogeneración y Servicios (the new productive state-owned subsidiaries of Petróleos Mexicanos formed on June 1, 2015) have assumed, effective as of June 1, 2015, all of the rights and obligations of Pemex-Exploración y Producción (a decentralized public entity and former subsidiary of Petróleos Mexicanos that was dissolved as of June 1, 2015) under the Guaranty Agreement and the Certificates of Designation as a matter of Mexican law and (iv) that, except for the succession of Pemex Exploración y Producción and Pemex Cogeneración y Servicios to the rights and obligations of Pemex-Exploración y Producción, which occurred as a matter of Mexican law, the Guaranty Agreement has not been amended or terminated since the date of its execution and there are no dealings or arrangements among the parties that would alter the terms of the Guaranty Agreement since its date of execution.

Based on the foregoing, and subject to the further assumptions and qualifications set forth below, it is our opinion that when the 2020 New Notes, the 2025 New Notes, the 2026 New Notes, the 2044 New Bonds and the 2046 New Bonds, in the forms filed as Exhibits 4.17, 4.18, 4.19, 4.20 and 4.21, respectively, to the Registration Statement have been duly executed by the Issuer and authenticated by the Trustee in accordance with the Indenture, and duly issued and delivered by the Issuer in exchange for an equal principal amount of 2020 Old Notes, the 2025 Old Notes, the 2026 Old Notes, the 2044 Old Bonds and the 2046 Old Bonds, respectively, (a) the New Securities will be valid, binding and enforceable obligations of the Issuer, entitled to the benefits of the Indenture and (b) assuming due authorization, execution and delivery by the Issuer of Certificates of Designation in form and substance sufficient under Mexican law to designate the Indenture and the New Securities as obligations of the Issuer entitled to the benefits of the Guaranty Agreement, the payment obligations of the Guarantors under their guaranties of the New Securities pursuant to the Guaranty Agreement, will constitute the valid, binding and enforceable obligations of each Guarantor.

Insofar as the foregoing opinion relates to the validity, binding effect or enforceability of any agreement or obligation of the Issuer or any Guarantor, (a) we have assumed that the Issuer or such Guarantor, as the case may be, and each other party to such agreement or obligation, has satisfied those legal requirements that are applicable to it to the extent necessary to make such agreement or obligation enforceable against it (except that no such assumption is made as to the Issuer or any Guarantor regarding matters of the federal law of the United States of America or the law of the State of New York that in our experience normally would be applicable to general business entities with respect to such agreement or obligation), (b) such opinion is subject to applicable bankruptcy, insolvency and similar laws affecting creditors’ rights generally and to general principles of equity and (c) such opinion is subject to the effect of judicial application of foreign laws or foreign governmental actions affecting creditors’ rights. In addition, we note (i) that the enforceability in the United States of the waiver by the Issuer of its immunities from court jurisdiction and from legal process, as set forth in the Indenture and the New Securities, is subject to the limitations imposed by the United States Foreign Sovereign Immunities Act of 1976 and (ii) that the designation in Section 1.13 of the Indenture of the U.S. federal courts sitting in The City of New York as the venue for actions or proceedings relating to the Indenture and the New Securities is (notwithstanding the waiver in or pursuant to Section 1.13 of the Indenture) subject to the power of such courts to transfer actions pursuant to 28 U.S.C. § 1404(a) or to dismiss such actions or proceedings on the grounds that such federal court is an inconvenient forum for such action or proceeding.

The foregoing opinion is limited to the federal law of the United States of America and the law of the State of New York.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Registration Statement and to the reference to this firm in the Registration Statement and the related prospectus under the caption “Validity of Securities.” In giving such consent, we do not thereby admit that we are experts with respect to any part of the Registration Statement, including this Exhibit, within the meaning of the term “expert” as used in the Act or the rules and regulations of the Commission issued thereunder. The opinions expressed herein are rendered on and as of the date hereof, and we assume no obligation to advise you, or to make any investigations, as to any legal developments or factual matters arising subsequent to the date hereof that might affect the opinions expressed herein.


Very truly yours,

CLEARY GOTTLIEB STEEN & HAMILTON LLP

By:		/S/ JORGE U. JUANTORENA
		Jorge U. Juantorena, a Partner