A 2012 Congressional Research Service report, “Financial Performance of the Major Oil Companies, 2007-2011”(PDF), analyzes the business results of the five biggest firms operating in the U.S. market: ExxonMobil, Chevron, BP, Royal Dutch Shell and ConocoPhillips. The report notes that their combined revenues in 2011 were equivalent to more than 10% of U.S. gross domestic product.