The USGS updated its assessment, saying the Bakken play has an estimated 3.65 billion barrels of oil while the Three Forks formation holds an estimated 3.73 billion barrels of oil. That's nearly twice the previous estimate from 2008.
For natural gas, the reserve estimate is almost triple what was reported five years ago. The plays are estimated to contain a combined 6.7 trillion cubic feet of undiscovered natural gas.
"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.
The United States is a world leader in natural gas reserves. In terms of imports, the U.S. Energy Department reported the bulk of its oil is from Canada.