MPLX (MPLX) CEO Mannen logs unit grant and tax-withholding dispositions

Rhea-AI Filing Summary

MPLX LP director and Chairman, President & CEO Maryann T. Mannen reported several equity transactions in common units. On March 1, 2026, she acquired 52,817 common units as a grant or award at a stated price of $0.0000 per unit. On March 2, 2026, she had three tax-withholding dispositions totaling several thousand units at $59.2200 per unit, used to satisfy exercise price or tax liabilities rather than open-market sales. Following these transactions, her direct holdings in MPLX common units remained significant, with reported balances after each step in the sequence.

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

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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^*

Mannen Maryann T.

(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
X	Officer (give title below)		Other (specify below)
	Chairman, President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
03/01/2026

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)	03/01/2026		A		52,817	A	$0	178,679	D
Common Units (Limited Partner Interests)	03/02/2026		F		3,407	D	$59.22	175,272	D
Common Units (Limited Partner Interests)	03/02/2026		F		3,404	D	$59.22	171,868	D
Common Units (Limited Partner Interests)	03/02/2026		F		6,409	D	$59.22	165,459	D

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:

Remarks:

The Reporting Person is a Chairman of the Board, President and Chief Executive Officer 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 Maryann T. Mannen	03/03/2026
	** 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).
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FAQ

What insider transactions did MPLX (MPLX) report for Maryann T. Mannen?

MPLX reported that Maryann T. Mannen, Chairman, President & CEO, received a grant of 52,817 common units and had three tax-withholding dispositions on March 2, 2026. These transactions adjusted her equity holdings without indicating open-market buying or selling activity.

How many MPLX units were granted to Maryann T. Mannen in this Form 4?

Maryann T. Mannen was granted 52,817 MPLX common units on March 1, 2026. The transaction was coded as a grant or award acquisition with a stated price of $0.0000 per unit, reflecting equity-based compensation rather than a market purchase.

What is the nature of the tax-withholding dispositions disclosed for MPLX (MPLX)?

The filing shows three transactions coded "F" as tax-withholding dispositions on March 2, 2026 at $59.2200 per unit. These units were delivered to cover exercise price or tax liabilities, not as open-market sales to third-party buyers.

Did Maryann T. Mannen buy or sell MPLX units on the open market?

The reported transactions do not show open-market buys or sells. Instead, they include a grant of 52,817 common units and three "F" code tax-withholding dispositions used to satisfy exercise price or tax liabilities, according to the transaction descriptions.

How did these Form 4 transactions affect Maryann T. Mannen’s MPLX holdings?

After the grant and subsequent tax-withholding dispositions, the Form 4 lists direct ownership balances after each step, with holdings remaining in the six-figure range. The sequence reflects compensation and tax-settlement activity rather than a full exit from MPLX equity exposure.