More than seven billion barrels of undiscovered shale oil are technically recoverable in three northern Plains states of the US.
Along with three times as much natural gas, this discovery represents twice as much oil as the federal government previously estimated.
The "tight" oil has been discovered as a result of new technology and a recent study of the Williston Basin, an area the size of West Virginia that spans portions of Montana, North and South Dakota. Extraction of the oil, which is trapped in relatively dense rock, requires the use of “fracking” and horizontal drilling techniques.
An earlier study of the Three Forks Formation in North Dakota by the Geological Survey revealed 3.7bn barrels of oil. However, a reassessment of the Bakken Formation, which lies above Three Forks, showed 3.6bn barrels, little more than a 2008 USGS estimate.
Although the oil is “technically recoverable”, it still may not be economically worth extracting immediately. But according to an adviser to the American Petroleum Institute (API production will be worthwhile in the near future due to innovations and efficiencies learnt from oil production in the Bakken Formation since the 1950s.