Document

We have acted as counsel for MPLX LP, a Delaware limited partnership (the “Partnership”), in connection with the authorization of the possible issuance and sale from time to time, on a delayed or continuous basis, by the Partnership of an indeterminate initial aggregate offering price or number of debt securities, common units representing limited partner interests in the Partnership and other classes of units representing limited partner interests in the partnership (together, the “Securities”), in each case as contemplated by the Partnership’s Registration Statement on Form S-3 to which this opinion is filed as an exhibit (as the same may be amended from time to time, the “Registration Statement”). The Securities may be offered and sold from time to time pursuant to Rule 415 under the Securities Act of 1933 (the “Securities Act”).

In connection with the opinions expressed herein, we have examined such documents, records and matters of law as we have deemed relevant or necessary for purposes of this opinion. In this examination, we have assumed the authenticity of all documents, the genuineness of signatures thereon, and the legal capacity of the signatories to sign on behalf of the entities for which they signed.

Based on the foregoing and subject to the further assumptions, qualifications and limitations set forth herein and in the Registration Statement, the statements in the Registration Statement under the caption “Material U.S. Federal Income Tax Consequences,” insofar as such statements purport to constitute summaries of U.S. federal income tax law or legal conclusions with respect thereto, constitute our opinion as to the material U.S. federal income tax consequences of the matters described therein.

Our opinion is based on the Internal Revenue Code of 1986, as amended, Treasury Regulations issued thereunder, Internal Revenue Service pronouncements, and judicial decisions, all as in effect on the date hereof, and all of which are subject to change or differing interpretation, possibly with retroactive effect. Further, our opinion is based on the facts, assumptions and representations set forth in the officer’s certificate regarding certain tax matters, executed as of the date hereof, and the Registration Statement, each as qualified by this opinion. If any of the facts, assumptions or representations is not true, correct or complete, our opinion


AMSTERDAM • ATLANTA • BEIJING • BOSTON • BRISBANE • BRUSSELS • CHICAGO • CLEVELAND • COLUMBUS • DALLAS DETROIT • DUBAI • DÜSSELDORF • FRANKFURT • HONG KONG • HOUSTON • IRVINE • LONDON • LOS ANGELES • MADRID MELBOURNE • MEXICO CITY • MIAMI • MILAN • MINNEAPOLIS • MUNICH • NEW YORK • PARIS • PERTH • PITTSBURGH SAN DIEGO • SAN FRANCISCO • SÃO PAULO • SHANGHAI • SILICON VALLEY • SINGAPORE • SYDNEY • TAIPEI • TOKYO • WASHINGTON

may not be relied upon. We undertake no responsibility to update this opinion or to advise you of any developments or changes as a result of a change in legal authority, fact, representation, assumption or document, or any inaccuracy in any fact, representation or assumption, upon which this opinion is based, or otherwise. Our opinion is not binding on the IRS or a court. The IRS may disagree with one or more of our conclusions, and a court may sustain the IRS's position.

We express no opinion on any issue relating to tax matters other than those U.S. federal income tax matters described herein, and we express no opinion as to the applicability or effect of other federal, foreign, state or local laws, or as to any matter not discussed herein.

We hereby consent to the filing of this opinion as Exhibit 8.1 to the Registration Statement and to the reference to Jones Day under the caption “Legal Matters” in the prospectus constituting a part of the Registration Statement. In giving such consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Securities and Exchange Commission promulgated thereunder.


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			May 6, 2026


			Very truly yours,

			/s/ Jones Day