Proven crude oil and lease-condensate reserves in the United States increased 9.3 percent to 36.5 billion barrels in 2013, up from 33.4 billion barrels in 2012, the U.S. Energy Information Administration said in a report Thursday.
That was the fifth year in a row of increases, with reserves exceeding 36 billion barrels for the first time since 1975, EIA said.
It also said proven wet natural gas reserves rose 9.7 percent to a record 354 trillion cubic feet in 2013, up from 322.7 tcf in 2012.
EIA said the increase in gas reserves was spurred by a rise in the average price for the fuel to $3.66 per million British thermal units in 2013 from $2.75 in 2012, which encouraged energy companies to drill for gas in fields that were not considered economic in 2012.
Proved reserves of crude oil and lease condensate in North Dakota, meanwhile, surpassed those in the federal Gulf of Mexico in 2013, ranking it second only to Texas among U.S. states, EIA said.
Collectively, North Dakota and Texas accounted for 90 percent of the overall net increase in U.S. proved oil reserves in 2013.
Tight oil plays accounted for 28 percent of all U.S. crude oil and lease condensate proved reserves, EIA said, noting the Bakken/Three Forks play covering parts of North Dakota, Montana and South Dakota regained its position as the largest tight oil play in the nation.
The Marcellus shale in Pennsylvania and West Virginia accounted for 70 percent of the increase in proved gas reserves. The increase in Pennsylvania alone was 13.5 tcf, the largest increase in the nation.
While U.S. oil and gas reserves and production increased in 2013, EIA said imports of both crude and gas declined by near 10 percent and 8 percent, respectively.