[Form 4] MPLX LP Insider Trading Activity

Rhea-AI Filing Summary

Garry L. Peiffer, a director of MPLX GP LLC (the general partner of MPLX LP), reported an acquisition of 1,157.128 common units of MPLX on 08/15/2025. The reported transaction lists a price of $0. After the transaction, the filing shows 61,644.675 common units beneficially owned directly and 68,497 beneficially owned indirectly by the Garry L. Peiffer Revocable Trust. The Form 4 was signed by an attorney-in-fact on 08/19/2025.

Positive

• Increased disclosed ownership: Reporting person acquired 1,157.128 common units, raising transparency around insider holdings.
• Clear ownership breakdown: Filing specifies direct holdings (61,644.675 units) and indirect holdings via a revocable trust (68,497 units).

Negative

• None.

Insights

Securities Analyst

TL;DR: Director reported a small acquisition and maintains both direct and indirect holdings; transaction details are limited.

The Form 4 documents a reported acquisition of 1,157.128 common units at a listed price of $0, increasing the reporting person's disclosed direct and indirect total holdings to 61,644.675 and 68,497 units respectively. The filing identifies the indirect holdings as held by the reporting person's revocable trust and notes the reporting person is a director of the issuer's general partner. This disclosure is routine for insiders and provides transparency on ownership but lacks detail on the nature of the $0 consideration.

Corporate Governance Expert

TL;DR: Insider disclosure confirms director ownership structure and a trustee-held indirect position; no material governance change disclosed.

The filing clarifies that the reporting person serves as a director of MPLX GP LLC and that part of his beneficial ownership is indirect through a revocable trust. The Form 4 provides required Section 16 transparency about changes in ownership. There is no information in the filing indicating any change in governance, control, or related-party arrangements beyond the routine update of holdings.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Peiffer Garry L.

(Last) (First) (Middle)

C/O MPLX LP

200 E. HARDIN STREET

(Street)

FINDLAY OH 45840

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
MPLX LP [ MPLX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
08/15/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Units (Limited Partner Interests)	08/15/2025		A		1,157.128	A	$0	61,644.675	D
Common Units (Limited Partner Interests)								68,497	I	By Revocable Trust(1)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. By Garry L. Peiffer Revocable Trust.

Remarks:

The Reporting Person is a Director of MPLX GP LLC, the general partner of the Issuer. The Issuer is managed by the directors and executive officers of MPLX GP LLC.

	/s/ Molly R. Benson, Attorney-in-Fact for Garry L. Peiffer	08/19/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did MPLX director Garry L. Peiffer report on Form 4?

He reported acquiring 1,157.128 common units of MPLX on 08/15/2025, with the filing signed on 08/19/2025.

How many MPLX units does Garry L. Peiffer beneficially own after the transaction?

61,644.675 units directly and 68,497 units indirectly via the Garry L. Peiffer Revocable Trust, per the Form 4.

What price was reported for the MPLX units acquired on 08/15/2025?

The reported price was $0 in the transaction entry on the Form 4.

What is the reporting person's relationship to MPLX?

He is a director of MPLX GP LLC, which is the general partner of the issuer, MPLX LP, as stated in the filing.

Was the Form 4 signed by the reporting person?

The form was signed by an attorney-in-fact, Molly R. Benson, for Garry L. Peiffer on 08/19/2025.