Hedge fund Elliott Management, which owns about 4 percent of Marathon Petroleum Corp, urged the refiner to conduct a strategic review and consider splitting into three businesses, Reuters reported.
Marathon should consider separating its chain of gasoline and convenience stores or break into three businesses, focused on retailing, refining and midstream operations that hold pipeline and storage assets, Elliott said on Monday.
Marathon shares were up 4 percent at $45.02 in early trading.
The activist investor, which also called the company "severely undervalued", said Marathon Petroleum could also look at transferring assets, which could go into a master limited partnership, to MPLX LP.
"Marathon's undervaluation is most glaring when the value of its three businesses is summed together," Quentin Koffey, a portfolio manager at Elliott, said in a letter to Marathon's board.
Elliott said its recommendations could help the company generate $14 billion-$19 billion for shareholders and boost the stock by more than 80 percent.
Marathon said last month it would transfer some assets into MPLX, the master limited partnership that it created in 2012.
The move came after activist hedge fund Jana Partners, which raised its stake in Marathon Petroleum to about 0.8 percent last week, pushed the company to separate its pipeline and other midstream assets.
Jana's managing partner, Barry Rosenstein, said in October he supported the shift of assets to MPLX and the possible changes to Marathon's financial reporting that would result.
Up to Friday's close, Marathon Petroleum shares had fallen about 16.5 percent this year.