X0306 4 2021-05-06 0 0001552000 MPLX LP MPLX 0001313785 Floerke Gregory Scott C/O MPLX LP 200 E. HARDIN STREET FINDLAY OH 45840 0 1 0 0 Exec. VP and COO Common Units (Limited Partner Interests) 2021-05-06 4 S 0 2500 27.00 D 83923 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 10,2020. The Reporting Person is the Executive Vice President and Chief Operating 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 Gregory S. Floerke 2021-05-10