<P> In April 2008, the USGS released a report giving a new resource assessment of the Bakken Formation underlying portions of Montana and North Dakota . The USGS believes that with new horizontal drilling technology there is somewhere between 3.0 and 4.5 billion barrels (480 × 10 ^ and 720 × 10 ^ m) of undiscovered, technically recoverable oil in this 200,000 square miles (520,000 km) formation that was initially discovered in 1951 . If accurate, this reassessment would make it the largest "continuous" oil accumulation (The USGS uses "continuous" to describe accumulations requiring extensive artificial fracturing to allow the oil to flow to the borehole) ever discovered in the U.S. The formation is estimated to contain significantly more - figures in excess of 150 billion barrels (2.4 × 10 m) have been reported - but it is yet uncertain how much of this oil is recoverable using current technology . In 2011, Harold Hamm claimed that the recoverable share may reach 24 billion barrels (3.8 × 10 m); this would mean that Bakken contains more extractable petroleum than all other known oil fields in the country, combined . </P> <P> The United States has the largest known deposits of oil shale in the world, according to the Bureau of Land Management and holds an estimated 2.175 trillion barrels (345.8 km) of potentially recoverable oil . Oil shale does not actually contain oil, but a waxy oil precursor known as kerogen . There is no significant commercial production of oil from oil shale in the United States . </P> <P> There are significant volumes of heavy oil in the oil sands of northeast Utah . There has yet to be any significant production from these deposits . </P>

Some of the largest oil reserves in the united states are located in