A vast geologic formation in three northern Plains states contains twice as much oil and three times as much natural gas as the federal government previously estimated, according to a reassessment of the area released by the Interior Department Tuesday.

Advances in technology and a new study of the Williston Basin, an area the size of West Virginia that spans portions of Montana, North Dakota and South Dakota, show that 7.4 billion barrels of undiscovered shale oil, also known as “tight” oil, are technically recoverable, according to the study released by the U.S. Geological Survey.

“These world-class formations contain even more energy resource potential than previously understood, which is important information as we continue to reduce our nation’s dependence on foreign sources of oil,” Interior Secretary Sally Jewell said in a prepared statement.

Tight oil is trapped in the pores of relatively dense rock and requires the use of hydraulic fracturing, or “fracking,” a controversial practice that some environmental organizations oppose. It also must be extracted using horizontal drilling techniques.

The doubling of the estimate resulted largely because of the first look at the Three Forks Formation in North Dakota, which the Geological Survey said contains 3.73 billion barrels of oil. Its reassessment of the Bakken Formation, which lies above Three Forks, showed 3.65 billion barrels, only a little more than a 2008 USGS estimate.

The agency’s conclusion that the formations contain 6.7 trillion cubic feet of natural gas and 530 million barrels of natural gas liquids represented a tripling of previous estimates.

On its Web site, Continental Resources, the largest leaseholder in the area, estimates that there are 20 billion barrels of “crude oil equivalent” in the Bakken and Three Forks formations.

The United States consumes 6.9 billion barrels of oil each year. Less than 40 percent now comes from foreign sources, the lowest proportion since 1988, Jewell said.

Officials hastened to note that “technically recoverable” oil may not be economically worth extracting, at least for now. But Richard Ranger, senior policy adviser to the American Petroleum Institute, said that innovations and efficiencies developed in producing oil from the Bakken Formation since the 1950s will make production worthwhile soon.

“I would argue that’s happening as we speak,” Ranger said.