Exhibit 5.1

February 7, 2025

Mach Natural Resources LP

14201 Wireless Way, Suite 300

Oklahoma City, Oklahoma 73134

We are acting as special counsel to Mach Natural Resources LP, a Delaware limited partnership (the “Partnership”), in connection with (i) the registration under the Securities Act of 1933, as amended (the “Act”), on a Registration Statement on Form S-3 (Registration No. 333-283511) initially filed with the Securities and Exchange Commission (the “Commission”) on November 27, 2024 and declared effected by the Commission on December 9, 2024 (such Registration Statement, as amended or supplemented, the “Registration Statement”).

Pursuant to the Registration Statement, the Partnership will issue up to 14,838,709 common units representing limited partner interests in the Partnership (the “Common Units”), including 1,935,483 Common Units to cover the underwriters’ option to purchase additional Common Units, if any, pursuant to that certain underwriting agreement, dated February 6, 2025 (the “Underwriting Agreement”), among the Partnership, Mach Natural Resources GP LLC, a Delaware limited liability company and the general partner of the Partnership (the “General Partner”), Stifel, Nicolaus & Company, Incorporated, Raymond James & Associates, Inc., TCBI Securities, Inc., doing business as Texas Capital Securities, and Truist Securities, Inc., on behalf of themselves and each of the other underwriters named in Schedule I thereto. The term “Common Units” shall include any additional common units registered by the Partnership pursuant to Rule 462(b) under the Act in connection with the offering contemplated by the Registration Statement.

In that connection, we have examined originals, or copies certified or otherwise identified to our satisfaction, of such documents, corporate records and other instruments as we have deemed necessary for the purpose of this opinion, including (i) the limited partnership and organizational documents of the Partnership, including the Amended and Restated Agreement of Limited Partnership of the Partnership (as amended by Amendment No. 1 dated as of June 13, 2024) (the “Partnership Agreement”) and the Amended and Restated Limited Liability Company Agreement of Mach Natural Resources GP LLC, the General Partner (the “GP LLC Agreement”), (ii) the Underwriting Agreement, (iii) minutes and records of the limited partnership proceedings of the Partnership with respect to the issuance of the Common Units, (iv) the Registration Statement and the exhibits thereto, (v) the base prospectus, dated December 9, 2024, which forms part of and is included in the Registration Statement (the “Base Prospectus”), (vi) the Base Prospectus, as supplemented by the Partnership’s preliminary prospectus supplement dated February 5, 2025 (the “Preliminary Prospectus”), relating to the offering of the Common Units and (vii) the Base Prospectus, as supplemented by the Partnership’s final prospectus supplement, dated February 6, 2025 (the “Final Prospectus”), relating to the offering of the Common Units.

For purposes of this letter, we have assumed the authenticity of all documents submitted to us as originals, the conformity to the originals of all documents submitted to us as copies and the authenticity of the originals submitted to us as copies. We have also assumed the legal capacity of all natural persons, the genuineness of the signatures of persons signing all documents in connection with which this opinion is rendered, the authority of such persons signing on behalf of the parties thereto, and the due authorization, execution and delivery of all documents by the parties thereto other than the Partnership. As to any facts material to the opinions expressed herein which we have not independently established or verified, we have relied upon statements and representations of officers and other representatives of the Partnership and others.

Based upon and subject to the qualifications, assumptions and limitations and the further limitations set forth herein, and having regard for such legal considerations as we have deemed relevant, we are of the opinion that the Common Units when issued by the Partnership against payment therefor in the circumstances contemplated by the Underwriting Agreement and in accordance with the Partnership Agreement and GP LLC Agreement, will be duly authorized, validly issued, fully paid and non-assessable.

Our opinion expressed above are subject to the qualifications that we express no opinion as to the applicability of, compliance with, or effect of (i) any bankruptcy, insolvency, reorganization, fraudulent transfer, fraudulent conveyance, moratorium or other similar law affecting the enforcement of creditors’ rights generally, (ii) general principles of equity (regardless of whether enforcement is considered in a proceeding in equity or at law), (iii) public policy considerations which may limit the rights of parties to obtain certain remedies, and (iv) any laws except the Delaware Revised Uniform Limited Partnership Act (the “Delaware Act”). In addition, we do not express any opinion as to the enforceability of any rights to contribution or indemnification which may be violative of public policy underlying any law, rule or regulation (including federal or state securities law, rule or regulation) or the enforceability of any so-called fraudulent conveyance or fraudulent transfer “savings clause” (and any similar provision in any other document or agreement) to the extent such provisions purport to limit the amount of the obligations of any party or the right to contribution of any other party with respect to such obligations.

We do not find it necessary for the purposes of this opinion, and accordingly we do not purport to cover herein, the application of the securities or “Blue Sky” laws of the various states to the issuance of the Common Units.

This opinion is limited to the specific issues addressed herein, and no opinion may be inferred or implied beyond that expressly stated herein. We assume no obligation to revise or supplement this opinion should the Delaware Act be changed by legislative action, judicial decision or otherwise.

This opinion is furnished to you in connection with the filing of the Partnership’s Current Report on Form 8-K, which is incorporated by reference into the Registration Statement, and in accordance with the requirements of Item 601(b)(5) of Regulation S-K promulgated under the Act, and is not to be used, circulated, quoted or otherwise relied upon or otherwise referred to by any other person for any other purpose. No opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement, other than as to the specific issues addressed herein, and no opinion may be inferred or implied beyond that expressly stated herein.

We hereby consent to the filing of this opinion with the Commission as Exhibit 5.1 to the Partnership’s Current Report on Form 8-K and its incorporation into the Registration Statement. We also consent to the reference to our firm under the heading “Legal Matters” in the Preliminary Prospectus and Final Prospectus. In giving this consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission.