The biggest U.S. petroleum company based on market value is ExxonMobil Corporation as of 2015. ExxonMobil, Chevron, ConocoPhillips, Occidental Petroleum and Eog Resources make the top five U.S. petroleum companies.
Comparing the market value of U.S. petroleum companies, ExxonMobil is the biggest one, and it is also the third-largest publicly traded company by market capitalization as of 2015. Chevron Corporation is one of the successor companies of Standard Oil, and it is engaged in the oil, natural gas and geothermal energy industries. ConocoPhillips is the world's largest independent pure play exploration and petroleum production company.
Other companies among the top ten biggest U.S. petroleum companies include Anadarko Petroleum, Phillips 66, Valero Energy, Marathon Petroleum and Devon Energy.