Exhibit 99.1

Marathon Petroleum Corporation Reports Second-Quarter 2013 Results

FINDLAY, Ohio, Aug. 1, 2013 – Marathon Petroleum Corporation (NYSE: MPC) today reported second-quarter earnings of $593 million, or $1.83 per diluted share, compared with $814 million, or $2.38 per diluted share, in the second quarter of 2012. For the second quarter of 2013, earnings adjusted for special items were $632 million, or $1.95 per diluted share, compared with earnings adjusted for special items of $867 million, or $2.53 per diluted share, for the second quarter of 2012.

“Our second-quarter earnings reflect a strong operating performance by our seven refineries despite some challenging market conditions,” said President and Chief Executive Officer Gary R. Heminger. “Our upgraded Detroit refinery and our recently acquired Galveston Bay refinery continue to operate well, and our Speedway and Pipeline Transportation segments both had excellent quarters financially.”

Heminger said that although MPC’s refinery throughputs and overall costs were in line with the company’s expectations, a number of factors reduced earnings compared to the strong financial results for the second quarter of last year. “Narrower crude oil price differentials affected our earnings,” he said. “In addition, our product price realizations compared to spot market values were lower in the second quarter of this year due in part to volatility in the Chicago market and compliance with the Renewable Fuel Standard.”

Heminger also noted MPC’s continuing shareholder focus in the second quarter. “We paid $113 million in dividends and purchased $882 million of common stock during the second quarter as part of our commitment to return capital to shareholders,” he said. “The recent announcement that we have increased our dividend by 20 percent reflects our confidence in the business and further underscores our commitment to total shareholder return over the long term.” MPC’s remaining share repurchase authorization was approximately $1.3 billion as of June 30.

Segment Results

Total income from operations was $960 million in the second quarter of 2013, compared with $1.31 billion in the second quarter of 2012.

Refining & Marketing

Refining & Marketing segment income from operations was $903 million in the second quarter of 2013, compared with $1.33 billion in the second quarter of 2012. The decrease was primarily due to a $4.95 per barrel reduction in the Refining & Marketing gross margin, which was $6.18 per barrel in the second quarter of 2013, compared with $11.13 per barrel in the second quarter of 2012. MPC’s benchmark Light Louisiana Sweet (LLS) crack spread was higher in the second quarter of 2013 compared to the second quarter of 2012. However, MPC experienced lower product price realizations compared to the spot market product prices used in the LLS crack spread calculation. The company believes the product price realizations were impacted by volatility in the Chicago market and compliance with the Renewable Fuel Standard. In addition, MPC’s average crude oil acquisition discount narrowed compared to LLS in the second quarter of 2013. The decrease in the Refining & Marketing gross margin was partially offset by higher refinery throughputs and sales volumes, attributable in large part to the Galveston Bay refinery, which was acquired on Feb. 1, 2013. The Refining & Marketing refined product sales volume was 2.13 million barrels per day (bpd) in the second quarter of 2013, compared with 1.57 million bpd in the second quarter of 2012.

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Speedway

Speedway segment income from operations was $123 million in the second quarter of 2013, compared with $107 million in the second quarter of 2012. The $16 million increase was primarily the result of a higher gasoline and distillate gross margin and merchandise gross margin, partially offset by higher expenses associated with the increase in the number of stores operated. Speedway gasoline and distillate gross margin per gallon averaged 17.38 cents in the second quarter of 2013, compared with 16.39 cents in the second quarter of 2012.

Pipeline Transportation

Pipeline Transportation segment income from operations was $58 million in the second quarter of 2013, compared with $50 million in the second quarter of 2012. The second-quarter 2013 segment income includes 100 percent of the operations of MPLX LP (NYSE: MPLX), a midstream master limited partnership formed by MPC in 2012. The increase in segment income was primarily due to an increase in transportation revenue, partially offset by an increase in operating and depreciation expenses.

Corporate and Special Items

Corporate and other unallocated expenses of $64 million in the second quarter of 2013 were $28 million lower than in the second quarter of 2012. The decrease was primarily due to a reduction in net employee benefit expenses, including lower pension expenses resulting from a pension plan amendment adopted in May 2012. During the second quarter of 2013, MPC recorded pretax pension settlement expenses of $60 million resulting from the level of employee lump sum retirement distributions occurring in 2013, compared with $83 million of pension settlement expenses in the second quarter of 2012.

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Strong Financial Position and Liquidity

On June 30, 2013, the company had $3.1 billion in cash and cash equivalents, an unused $2.5 billion revolving credit agreement and a $1 billion unused trade receivables securitization facility. The company’s credit facilities and cash position should provide it with sufficient flexibility to meet its day-to-day operational needs and continue its balanced approach to investing in the business and returning capital to shareholders. As of June 30, 2013, the company’s strong financial position was further reflected by its debt-to-total-capital ratio of 22 percent.

Conference Call

At 10 a.m. EDT today, MPC will hold a webcast and conference call to discuss the earnings release and provide an update on company operations. Interested parties may listen to the conference call on MPC’s website at http://www.marathonpetroleum.com by clicking on the “2013 Second-Quarter Financial Results” link. Replays of the conference call will be available on the company’s website through Thursday, Aug. 15. Financial information, including the earnings release and other investor-related material, will also be available online prior to the webcast and conference call at http://ir.marathonpetroleum.com in the Quarterly Investor Packet and Earnings Capsule.

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About Marathon Petroleum Corporation

MPC is the nation’s fourth-largest refiner, with a crude oil refining capacity of approximately 1.7 million barrels per calendar day in its seven-refinery system. Marathon brand gasoline is sold through approximately 5,000 independently owned retail outlets across 17 states. In addition, Speedway LLC, an MPC subsidiary, owns and operates the nation’s fourth-largest convenience store chain, with approximately 1,470 convenience stores in nine states. MPC also owns, leases or has ownership interests in approximately 8,300 miles of pipeline. Through subsidiaries, MPC owns the general partner of MPLX LP, a midstream master limited partnership. MPC’s fully integrated system provides operational flexibility to move crude oil, feedstocks and petroleum-related products efficiently through the company’s distribution network in the Midwest, Southeast and Gulf Coast regions. For additional information about the company, please visit our website at http://www.marathonpetroleum.com.

Investor Relations Contacts:

Pamela Beall (419) 429-5640

Beth Hunter (419) 421-2559

Media Contacts:

Angelia Graves (419) 421-2703

Jamal Kheiry (419) 421-3312

References to Earnings

References to earnings mean net income attributable to Marathon Petroleum Corporation (MPC) from the statements of income. Unless otherwise indicated, references to earnings, earnings adjusted for special items and earnings per share are MPC’s share after excluding amounts attributable to noncontrolling interests.

Non-GAAP Financial Information

In addition to earnings determined in accordance with GAAP, MPC has provided supplemental “earnings adjusted for special items,” a non-GAAP financial measure that facilitates comparisons to earnings forecasts prepared by stock analysts and other third parties. Such forecasts generally exclude the effects of items that are considered non-recurring, are difficult to predict or to

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measure in advance or that are not directly related to MPC’s ongoing operations. A reconciliation between GAAP earnings and “earnings adjusted for special items” is provided in a table on page 1 of this release. “Earnings adjusted for special items” should not be considered a substitute for earnings as reported in accordance with GAAP. We believe certain investors use “earnings adjusted for special items” to evaluate MPC’s financial performance between periods. Management also uses “earnings adjusted for special items” to compare MPC’s performance to certain competitors.

Forward-looking Statements

This press release contains forward-looking statements within the meaning of federal securities laws. These forward-looking statements relate to, among other things, MPC’s expectations, estimates and projections concerning MPC business and operations. You can identify forward-looking statements by words such as “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “project,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. Such forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and other factors, some of which are beyond MPC’s control and are difficult to predict. Factors that could cause actual results to differ materially from those in the forward-looking statements include: volatility in and/or degradation of market and industry conditions; the availability and pricing of crude oil and other feedstocks; slower growth in domestic and Canadian crude supply; completion of pipeline capacity to areas outside the U.S. Midwest; consumer demand for refined products; transportation logistics; the reliability of processing units and other equipment; our ability to successfully implement growth opportunities; impacts from our repurchases of shares of MPC common stock under our share repurchase authorization, including the timing and amounts of any common stock repurchases; state and federal environmental, economic, health and safety, energy and other policies and regulations, including the cost of compliance with the Renewable Fuel Standard; other risk factors inherent to our industry; and the factors set forth under the heading “Risk Factors” in MPC’s Annual Report on Form 10-K for the year ended Dec. 31, 2012, filed with the Securities and Exchange Commission (SEC). In addition, the forward-looking statements included herein could be affected by general domestic and international economic and political conditions. Unpredictable or unknown factors not discussed here or in MPC’s Form 10-K could also have material adverse effects on forward-looking statements. Copies of MPC’s Form 10-K are available on the SEC website, MPC’s website at http://ir.marathonpetroleum.com or by contacting MPC’s Investor Relations office.

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Consolidated Statements of Income (Unaudited)

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Supplemental Statistics (Unaudited)

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Supplemental Statistics (Unaudited) (continued)

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Segment Earnings Before Interest, Taxes, Depreciation & Amortization (Segment EBITDA) (Unaudited)

Select Financial Data (Unaudited)

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