On November 15, 2013, Garry L. Peiffer, President and Director of MPLX GP LLC, the
general partner of MPLX LP, notified the Partnership he will retire as President effective
January 1, 2014. Mr. Peiffer will remain as a member of the Board of Directors of the General Partner. In light of Mr. Peiffer's leadership and service to the Partnership as its President in its first full year of operations, the General Partner took action to accelerate the vesting of his unvested restricted phantom units that would otherwise be forfeited upon his retirement.