(Bloomberg) -- Marathon Petroleum Corp. plans to repurchase as much as $10 billion of stock after the U.S. oil refiner completed the sale of its Speedway fuel retail chain.The plan starts with a cash tender offer to buy as much as $4 billion of shares, or about 10% of its current market value, the company said Friday. The repurchase would be the oil refiner’s biggest-ever share buyback, according to data compiled by Bloomberg.“After the completion of the tender offer, we intend to execute on the remainder of our $10 billion repurchase authorization over the subsequent 12 to 18 months,” Chief Financial Officer Maryann T. Mannen said in a statement. In addition, $2.5 billion of proceeds from the Speedway sale has been allocated to reduce long-term debt.Marathon shares jumped as much as 5.1% to $61.80, the highest since January 2020. That compares with a 3% gain in the S&P 500 Energy Index.Marathon agreed in March 2020 to sell Speedway to 7-Eleven Inc., a unit of Japan’s Seven & i Holdings Co., for $21 billion. The transaction followed months of pressure on Marathon from investors including Elliott Management Corp. and D.E. Shaw & Co. , pressing the company to make sweeping changes to improve its performance. Elliott had pushed for Marathon to break itself up into three separate businesses: refining, retail and pipelines.The deal’s after-tax cash proceeds are estimated at $16.5 billion, the company said.(Adds share price in fourth paragraph. An earlier version corrected the repurchase amount in first paragraph.)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.