#10 Marathon Petroleum
Ticker: MPC
YTD stock performance: 88%
Market cap: $21.3 billion
Fortune 500 rank: 31

Spun out of Marathon Oil (MRO, Fortune 500) in June 2011, Marathon Petroleum (MPC, Fortune 500) refines, markets, and transports oil through refineries in Illinois, Ohio, Michigan, Louisiana, Kentucky and Texas. The company also has a large retail presence in the Midwest.

Under pressure from activist investor Jana Partners, Marathon Petroleum spun off its pipeline operations, taking MPLX LP (MPLX) public in October. Since then, shares of that limited partnership have increased 41%. At Jana Partners' urging, Marathon Petroleum agreed to buy back $2 billion worth of shares in February as well.

The petroleum company also spent $2.5 billion to acquire BP's (BP) Texas City refinery, the site of a 2005 explosion that killed 15 workers. The company said the refinery is safe now, and analysts think it will give Marathon more room to expand in the growing Gulf Coast region.

The biggest concern is demand. Should a slowing economy dampen oil prices, Marathon Petroleum could take a big hit in 2013.

Source: CNNMoney
Data as of Dec. 7 market close, provided by S&P Capital IQ.
  @FortuneMagazine - Last updated December 19 2012 02:52 PM ET
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