There's been speculation for years about a western North Dakota formation known as the Bakken Shale.
The formation extends into Montana and Canada. Geologists have estimated the area holds hundreds of billions of barrels of oil.
"This is the largest oil accumulation in the lower 48. It is also the largest continuous type of oil accumulation that we have ever assessed."
The problem has been how to get that oil out of the ground. It's not a pool you drill down to because this oil is in the rocks. But new technology makes it easier to collect that oil.
The USGS study says with todays technology, about 4 billion barrels of oil can be pumped from the Bakken formation.
In an interview provided by USGS, scientist Brenda Pierce put the North Dakota oil in context.
"Of the current USGS estimates, this is the largest oil accumulation in the lower 48," Pierce says. "It is also the largest continuous type of oil accumulation that we have ever assessed."
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By comparison, the 4 billion barrels in North Dakota represent less than half the oil in the Arctic National Wildlife refuge which has an estimated 10 billion barrels of recoverable oil.
But Sen. Byron Dorgan (ND-D) says the 4 billion barrels in the Bakken Shale is only the beginning.
"We know there's a lot more oil in the Bakken Shale, so does the USGS," Dorgan says. "Under todays technology that cannot be recovered. With tomorrows technology it likely could."
Dorgan says the release of the USGS study should encourage more investment in pipelines, or perhaps a refinery in the state.
"It makes some sense and would provide some comfort I think to those who would like to make longer term investments, especially in an oil refinery. I hope our state would be interested and the private sector would be interested so we could have a new refinery or a very significant expansion of the refinery that exists," Dorgan says.
Oil companies are already working to drill hundreds of new wells in North Dakota. If oil prices stay high, it's likely the boom in North Dakotas oil patch will continue.