A new estimate from the department's Energy Information Administration said the United States ranks second behind Russia in recoverable shale oil reserves and fourth behind Algeria in natural gas contained in layers of shale rock.
The EIA estimated shale oil and gas reserves in the United States combined with reserves in 41 other nations now equal 10 percent of the world's crude oil reserves and 37 percent of its natural gas.
Shale is being produced commercially only in the United States and Canada; however, the EIA said there are other nations where supplies are ample. China is among the top four nations in both shale gas and oil reserves.
"As shale oil and shale gas production has grown in the United States to become 30 percent of oil and 40 percent of natural gas total production, interest in the oil and natural gas resource potential of shale formations outside the United States has also grown," EIA Administrator Adam Sieminski said in a written statement. "There is a significant potential for international shale oil and shale gas, though the extent to which technically recoverable shale resources will prove to be economically recoverable is not yet clear."
Along with the price of production, shale energy also faces potential limits due to concerns over the environmental impact of fracking and competition from low-priced coal.
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