The Three Forks formation in North Dakota, South Dakota and Montana could hold more undiscovered, technically recoverable oil than the Bakken Shale that lies above it, according to the United States Geological Survey’s (USGS) latest assessment.

The mean of the estimate for the two formations’ combined undiscovered, technically recoverable oil is 7.38 billion barrels, effectively doubling the 2008 estimate for the Bakken shale alone. The mean estimate for Bakken oil, at 3.65 bn bbls – the same as in 2008 – is just shy of the Three Forks’ 3.73 bn bbl estimate.

At the time of the 2008 assessment, the Three Forks was considered unproductive, but subsequent drilling and production results showed that it warranted a closer look, said the Department of the Interior (DOI). The Three Forks and Bakken have produced a combined 450 million bbls of oil since the USGS’ 2008 Bakken assessment.

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