A new report by the U.S. Energy Information Administration (EIA) found that U.S proven crude oil and natural gas reserves jumped for a fifth year in a row in 2013 to 36.5 billion barrels.
Proven crude reserves rose by 5.8 billion barrels in 2013, mostly thanks to extensions at existing unconventional drilling sites.
Texas saw the biggest spike in reserves, adding 2 billion barrels, while North Dakota added 1.6 billion barrels.
In 2013, 2.73 billion barrels of oil were produced in the United States including the Gulf of Mexico.
Natural gas reserves rose by 10 percent to a record 354 trillion cubic feet on the strength of rising development in the Marcellus shale play.
Natural gas production hit 26.5 trillion cubic feet in 2013.
West Virginia and Pennsylvania were the big winners for natural gas production, adding 13.5 trillion cubic feet and 8.3 trillion cubic feet of proven reserves respectively.
Shale finds accounted for 45 percent of new proven natural gas reserves and made up the majority of natural gas production in 2013.
The EIA said gains in 2013 did not completely offset large declines seen in 2012 suggesting that operators are “cautious” about committing to drilling natural gas prospects or are turning their attention to liquid rich sites.
The new estimate puts crude and natural gas proven reserves at their highest levels since 1975.