The formations, called Bakken and Three Forks, span much of western North Dakota, the northern tip of South Dakota and the northeastern tip of Montana. The last time the United States Geological Survey assessed this area for its oil and gas reserves was in 2008. But that assessment did not include the Three Forks formation, which explains the substantial increase in the estimates. USGS estimates that these two formations together hold 7.4 billion barrels of undiscovered—but technically recoverable—oil and 6.7 trillion cubic feet of natural gas.

The estimates were requested by Sen. John Hoeven, R-N.D., in early 2011. “This is clearly great news for North Dakota and great news for the nation,” Hoeven said in a statement. “It will further serve to enhance our state’s role as an energy powerhouse for the nation.”

The energy boom’s impact on North Dakota’s economy is undeniable. The state has the lowest unemployment in the country, at 3.3 percent. …

Nonetheless, the data add more hard evidence of America’s energy boom, which was largely unimaginable just seven years ago. The estimates also underline the opportunities, including economic benefits and energy security, and the challenges, especially President Obama’s commitment to tackle climate change, that come with a major fossil-fuel boom.