FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person *   MARKWEST HYDROCARBON L.L.C. 2. Date of Event Requiring Statement (Month/Day/Year) 09/01/2016 3. Issuer Name and Ticker or Trading Symbol MPLX LP [MPLX] (Last) (First) (Middle) 1515 ARAPAHOE STREET, TOWER 1, SUITE 1600 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) DENVER, CO 80202 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Class A Units 28,554,313 (1) (2) (3) I (1) (2) (3) See Footnotes (1) (2) (3) Common Units (Limited Partner Interests) 79,466,136 (1) (3) I (1) (3) See Footnotes (1) (3)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
MARKWEST HYDROCARBON L.L.C. 1515 ARAPAHOE STREET TOWER 1, SUITE 1600 DENVER, CO 80202	  X	  X	Â	Â

Signatures

/s/ Molly R. Benson, Director and Secretary of the Member, MPLX Holdings Inc.		09/06/2016
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(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).
(1)	Pursuant to a Master Reorganization Agreement effective September 1, 2016 by and among MarkWest Hydrocarbon, L.L.C. ("Hydrocarbon"), MarkWest Energy Partners, L.P., MWE GP LLC, MPLX LP ("MPLX"), MPLX GP LLC ("the "General Partner"), MPC Investment LLC ("MPC Investment"), MPLX Logistics Holdings LLC ("Logistics Holdings") and MPLX Holdings Inc. ("Holdings"), Hydrocarbon became a part of a reporting group which includes Marathon Petroleum Corporation ("MPC"), MPC Investment, the General Partner, Holdings and Logistics Holdings. MPC Investment, a direct wholly-owned subsidiary of MPC, owns all of the membership interests or stock in the General Partner, Logistics Holdings and Holdings. Holdings owned all of the membership interests in Hydrocarbon as of September 1, 2016. Accordingly, the General Partner, Logistics Holdings, Holdings and Hydrocarbon were all indirect wholly-owned subsidiaries of MPC as of September 1, 2016.
(2)	Hydrocarbon, a wholly-owned subsidiary of Holdings, owned all of the Issuer's Class A units as of September 1, 2016.
(3)	As of September 1, 2016, the General Partner directly owned 7,630,225 general partner units, representing its 2% general partner interest in the Issuer and Logistics Holdings beneficially owned 79,466,136 common units representing limited partnership interests in the Issuer. MPC Investment owns all of the membership interests in Logistics Holdings and the General Partner, and MPC owns all of the membership interest in MPC Investment. Accordingly, MPC, MPC Investment and Holdings may be deemed to have indirectly beneficially owned the securities directly held by the General Partner, Logistics Holdings and Hydrocarbon but disclaim beneficial ownership except to the extent of their respective pecuniary interests therein.

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