Exhibit 99.1 

UNAUDITED PRO FORMA CONSOLIDATED STATEMENT OF INCOME

On December 4, 2015, MPLX LP (“MPLX”), a midstream master limited partnership sponsored by Marathon Petroleum Corporation (“MPC”), announced that it completed the acquisition of MarkWest Energy Partners, L.P. (“MWE”), whereby a wholly-owned subsidiary of MPLX merged with and into MWE (the “Merger”), with MWE surviving the Merger as a wholly-owned subsidiary of MPLX.

On December 4, 2015, at the effective time of the Merger (the “Effective Time”), (a) each outstanding MWE common unit (the “MWE Common Units”) was converted into the right to receive 1.09 MPLX common units (the “MPLX Common Units” and/or the “Common Unit Merger Consideration”) and $6.20 in cash (the “Cash Consideration” and, together with the Common Unit Merger Consideration, the “Common Merger Consideration”) and (b) each outstanding MWE Class B unit was converted into the right to receive one MPLX Class B unit (the “MPLX Class B Units”). The MPLX Class B Units will convert in two equal installments on July 1, 2016 and July 1, 2017 (unless earlier converted upon a fundamental change regarding MPLX) into 1.09 MPLX Common Units and the right to receive the Cash Consideration. In connection with the Merger, MPC contributed approximately $1,230 million in cash to MPLX at the Effective Time for Cash Consideration paid to MWE unitholders, and will contribute approximately $50 million in cash to MPLX for the Cash Consideration to be paid upon the conversion of the MPLX Class B Units. These contributions are with respect to MPC’s existing interests in MPLX (including incentive distribution rights (“IDRs”)) and not in consideration of new units or other equity interest in MPLX. At the Effective Time, the MWE Class A units, all of which were owned by wholly-owned subsidiaries of MWE, converted into MPLX Class A units (the “MPLX Class A Units”). Since the MPLX Class A Units are owned by a wholly-owned subsidiary of MPLX, they are eliminated and have no impact on this unaudited pro forma consolidated statement of income.

As a result of the Merger, each phantom unit granted under MWE’s equity plans outstanding immediately prior to the Effective Time became fully vested and converted into an equivalent number of MWE Common Units, which were canceled and converted into the right to receive the Common Merger Consideration. As of the Effective Time, each MWE distribution equivalent right award was canceled and the holder thereof ceased to have any rights with respect thereto, other than the right to receive distributions declared or made (but not yet paid) by MWE prior to the Effective Time.

As a result of the completion of the Merger, as of the Effective Time, MPLX assumed an aggregate principal amount of $4.1 billion in senior notes issued by MWE and MarkWest Energy Finance Corporation consisting of: $750 million aggregate principal amount of 5.500% senior notes due February 15, 2023; $1.0 billion aggregate principal amount of 4.500% senior notes due July 15, 2023; $1.15 billion aggregate principal amount of 4.875% senior notes due December 1, 2024; and $1.2 billion aggregate principal amount of 4.875% senior notes due June 1, 2025 (collectively, the “MWE senior notes”). In connection with the Merger, MPLX commenced offers to exchange any and all outstanding MWE senior notes for (1) up to $4.1 billion aggregate principal amount of new notes issued by MPLX having the same maturity and interest rates as the MWE senior notes and (2) cash. Also in connection with the Merger, MWE’s bank revolving credit facility was terminated and approximately $943 million outstanding under that facility was repaid.

The unaudited pro forma consolidated statement of income for the year ended December 31, 2015, has been prepared to give effect to the Merger as if it had occurred on January 1, 2015, using the acquisition method of accounting with MPLX as the acquirer. The unaudited pro forma consolidated statement of income has been developed from and should be read in conjunction with the consolidated financial statements and related notes contained in MPLX’s Annual Report on Form 10-K for the year ended December 31, 2015, as well as the notes accompanying this unaudited pro forma consolidated statement of income.

Pro forma adjustments are included only to the extent they are (i) directly attributable to the Merger, (ii) factually supportable and (iii) expected to have a continuing impact on MPLX’s consolidated results. The accompanying unaudited pro forma consolidated statement of income is presented for illustrative purposes only and is based on available information and assumptions MPLX believes are reasonable. It does not purport to represent what the actual consolidated results of operations of MPLX would have been had the Merger occurred on January 1, 2015, nor is it necessarily indicative of future consolidated results of operations. The actual results of operations will differ, perhaps significantly, from the pro forma amounts reflected herein.

For purposes of this unaudited pro forma consolidated statement of income, giving effect to the consideration described above and approximately $5,075 million of debt assumed by MPLX, the aggregate consideration to complete the Merger was approximately $13,681 million. Accounting Standards Codification 805, “Business Combinations,” requires that the consideration transferred be measured at the market price as of the date of the Merger.

MPLX LP

Unaudited Pro Forma Consolidated Statement of Income

for the year ended December 31, 2015

See Notes to the Unaudited Pro Forma Consolidated Statement of Income.

Notes to the Unaudited Pro Forma Consolidated Statement of Income

Except as noted within the context of each footnote, the dollar amounts presented in the tabular data within these footnotes are stated in millions of dollars.

1. Basis of Pro Forma Presentation

The accompanying unaudited pro forma consolidated statement of income is intended to reflect the effect of the Merger on MPLX’s consolidated results and presents the pro forma consolidated results of operations of MPLX based on the historical consolidated financial statements of MPLX and MWE, after giving effect to the Merger and pro forma adjustments as described in these notes. Pro forma adjustments are included only to the extent they are (i) directly attributable to the Merger, (ii) factually supportable and (iii) expected to have a continuing impact on MPLX’s consolidated results. Certain items included in the historical consolidated financial statements of MPLX and MWE were not adjusted in this unaudited pro forma consolidated statement of income, as they were not directly related to the Merger, including debt refinancing and other historical changes to the capital structures, and recognized impairments of long-lived assets and goodwill.

The unaudited pro forma consolidated statement of income for the year ended December 31, 2015, has been prepared to give effect to the Merger as if it had occurred on January 1, 2015.

Fair Value Adjustments

The Merger was accounted for using the acquisition method of accounting with MPLX as the acquirer of MWE. The unaudited pro forma consolidated statement of income and accompanying notes reflect management’s estimate of fair values and useful lives assigned to the assets acquired and liabilities assumed and are subject to revision. Fair value estimates were determined based on discussions between MPLX and MWE management, due diligence efforts, information available in public filings and a third-party valuation (for substantially all of the assets acquired and liabilities assumed from MWE). MPLX is still completing its analysis of the final purchase price allocation for property, plant and equipment, intangibles and deferred taxes.

2. Purchase Price

The aggregate consideration reflected in the unaudited pro forma consolidated statement of income is approximately $13,681 million, including the fair value of MPLX Common Units issued of approximately $7,326 million, cash of approximately $1,230 million, payables of approximately $50 million and assumed debt of approximately $5,075 million. This amount was based on the outstanding MWE Common Units at December 3, 2015, on a fully-diluted basis, the Common Merger Consideration and the price per MPLX Common Unit of $32.63, as of the close of trading on December 3, 2015.

Purchase Price and Aggregate Consideration

3. Pro Forma Adjustments to the Unaudited Consolidated Statement of Income

MWE has a 60% legal ownership interest in MarkWest Utica EMG, L.L.C (“MarkWest Utica EMG”). MarkWest Utica EMG’s inability to fund its planned activities without subordinated financial support qualify it as a variable interest entity. The financing structure for MarkWest Utica EMG at its inception resulted in a de-facto agent relationship under which MWE was deemed to be the primary beneficiary of MarkWest Utica EMG. Therefore, MWE consolidated MarkWest Utica EMG in its historical financial statements. In the fourth quarter of 2015, based on economic conditions and other pertinent factors, the accounting for its investment in MarkWest Utica EMG was re-assessed. As of December 4, 2015, the entity has been deconsolidated. For purposes of this unaudited pro forma consolidated statement of income, MarkWest Utica EMG has been consolidated for the period prior to the acquisition consistent with its treatment in the historical periods presented.

A summary of the amounts included in the historical financial statements of MWE for the period from January 1, 2015, through December 3, 2015, related to MarkWest Utica EMG are as follows:

EMG Utica, LLC (“EMG Utica”), a joint venture partner, received a special non-cash allocation of income of approximately $41 million for the period from January 1, 2015 through December 3, 2015. Net income of MWE would not have changed had MarkWest Utica EMG been deconsolidated for the period from January 1, 2015 through December 3, 2015.

4. Pro Forma Net Income per Common Unit

The pro forma basic and diluted net income per limited partner unit is determined by dividing the limited partners’ interests in pro forma net income attributable to MPLX by the weighted-average number of common units outstanding for the period. As there is more than one class of participating securities, the two-class method is used when calculating the net income per unit applicable to limited partners. The classes of securities in the calculation include common units, class B units, subordinated units, general partner units, certain equity-based compensation awards and IDRs. Presented in the table below, all newly issued units in connection with the acquisition of MWE were assumed to have been outstanding for the entire period, net income attributable to the general partner, IDRs and limited partners was adjusted per the pro forma adjustments and the pro forma basic and diluted weighted average number of common units equals the actual weighted average number of common units outstanding for the year ended December 31, 2015, plus the amount of assumed newly issued common units.

5. The MWE Historical Financial Statements

The historical consolidated statement of income of MWE was derived from the consolidated financial statements included in MWE’s Quarterly Report on Form 10-Q for the period ended September 30, 2015 and internal results for the period from October 1, 2015 through December 3, 2015. The MWE historical consolidated statement of income as presented includes the following reclassifications to conform to MPLX’s financial statement presentation.