X0306 4 2019-08-09 0 0001552000 MPLX LP MPLX 0001521094 Peiffer Garry L. C/O MPLX LP 200 E. HARDIN STREET FINDLAY OH 45840 1 0 0 0 Common Units (Limited Partner Interests) 2019-08-09 4 P 0 18800 27.301 A 68497 I By Revocable Trust Common Units (Limited Partner Interests) 14302.313 D The price reported in Column 4 is a weighted average price. These units were purchased in multiple transactions at prices ranging from $27.265 to $27.31, inclusive. The Reporting Person undertakes to provide to MPLX LP, any security holder of MPLX LP, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of units purchased at each separate price within the range set forth in footnote (1) to this Form 4. By Garry L. Peiffer Revocable Trust. 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 2019-08-13