According to the US Crude Oil and Natural Gas Proved Reserves report issued yesterday, crude oil in the country rose for the fourth consecutive year in 2012 to 33 billion barrels.

In fact, crude oil and lease condensate proved reserves were the highest since 1976 and saw the largest annual increase since 1970.

The EIA put the increase down to increased exploration, improved technology for developing tight oil plays and sustained high historical crude oil prices.

Price is what let the industry down on the gas side of things, with low prices driving down natural gas proved reserves in 2012, ending a 14-year run of consecutive gas reserve increases.

Proved reserves are estimated using analysis of geological and engineering data to determine the resource amount that can be recovered with reasonable certainty in future years from known reservoirs and under existing economic and operating conditions.

With significant changes in year-to-year gas prices, the economic element of proving natural gas reserves has been affected, resulting in the decrease.

The 7.5% decrease in gas reserves in 2012 resulted in an evaluation of 323 trillion cubic feet, with the average natural gas price that year recorded as 34% below its 2011 level.

Despite the 2012 drop, the EIA said there was a 5% increase in production from 2011 to 2012.

That, along with higher prices in 2013 and technology advances, leads the EIA to expect to see an increase in reserves again for 2013.

Texas recorded the largest volumetric increase in proved oil reserves among the individual states in 2012, going up by 3Bbbl.

North Dakota had the second largest increase of 1.1Bbbl.