Washington and its European allies have hit Iran with economic sanctions targeting its energy sector as punishment for its controversial nuclear program. Western allies say Iran is using its nuclear program to develop a weapon, though Tehran maintains it has peaceful intentions.
The U.S. Government Accountability Office in a 26-page report found 16 companies ranging from the China National Petroleum Corp. to Italy's Edison remain active in the Iranian energy sector.
Foreign firms, however, have pulled back significantly from Iran, the report said. Of the 41 companies listed in a 2010 report, 20 were moving out of the Iranian energy sector. Those that withdrew said it was becoming too difficult to do business in Iran.
The report notes that although some companies are moving out, Indian and Chinese state oil companies are making up the difference.
The GAO report noted that it wasn't tasked with examining whether the companies doing business in Iran met the legal requirement for doing so under the Iran Sanctions Act nor was it making specific recommendations.
Iran ranks in the top three in the world in terms of oil and natural gas reserves. As of 2009, the report said, Iran received 66 percent of its total revenue from energy.