8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) February 9, 2023

MPLX LP

(Exact name of registrant as specified in its charter)

Delaware 001-35714 27-0005456

(State or other jurisdiction

of incorporation)

(Commission

File Number)

(IRS Employer

Identification No.)

200 E. Hardin Street, Findlay, Ohio45840

(Address of principal executive offices) (Zip code)

Registrant's telephone number, including area code:(419)421-2414

Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

Soliciting material pursuant to Rule 14a-12under the Exchange Act (17 CFR 240.14a-12)

Pre-commencementcommunications pursuant to Rule 14d-2(b)under the Exchange Act (17 CFR 240.14d-2(b))

Pre-commencementcommunications pursuant to Rule 13e-4(c)under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading

symbol(s)

Name of each exchange

on which registered

Common Units Representing Limited Partnership Interests MPLX New York Stock Exchange

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2of the Securities Exchange Act of 1934 (§240.12b-2of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01

Other Events.

MPLX LP (the "Issuer") is filing herewith the following exhibits to its Registration Statement on Form S-3(Registration No. 333-248443):

1.

Underwriting Agreement, dated as of February 2, 2023, by and among the Issuer, MPLX GP LLC, the general partner of the Issuer, and each of J.P. Morgan Securities LLC, BofA Securities, Inc. and MUFG Securities Americas Inc., acting as representatives of the several underwriters named therein;

2.

Twenty-Seventh Supplemental Indenture, dated as of February 9, 2023, by and between the Issuer and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Note);

3.

Twenty-Eighth Supplemental Indenture, dated as of February 9, 2023, by and between the Issuer and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Note); and

4.

Opinion of Jones Day.

Item 9.01

Financial Statements and Exhibits.

(d) Exhibits.

Exhibit
Number

Description

1.1 Underwriting Agreement, dated as of February 2, 2023, by and among the Issuer, MPLX GP LLC, the general partner of the Issuer, and each of J.P. Morgan Securities LLC, BofA Securities, Inc. and MUFG Securities Americas Inc., acting as representatives of the several underwriters named therein
4.1 Twenty-Seventh Supplemental Indenture, dated as of February 9, 2023, by and between the Issuer and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Note)
4.2 Twenty-Eighth Supplemental Indenture, dated as of February 9, 2023, by and between the Issuer and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Note)
5.1 Opinion of Jones Day
23.1 Consent of Jones Day (included in Exhibit 5.1)
104 Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

MPLX LP
By: MPLX GP LLC, its General Partner
Date: February 9, 2023 By:

/s/ Molly R. Benson

Name: Molly R. Benson
Title: Vice President, Chief Securities, Governance & Compliance Officer and Corporate Secretary

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MPLX LP published this content on 09 February 2023 and is solely responsible for the information contained therein. Distributed by Public, unedited and unaltered, on 09 February 2023 18:30:06 UTC.