Development in Pennsylvania's Marcellus Shale accounted for one-fifth of the nation's natural gas reserve increase in 2010, and the new numbers on how much gas is trapped in the formation lead one industry group to predict the Marcellus soon will be the new leader in domestic shale plays.
Nationwide, proved reserves of natural gas increased by the biggest year-over-year margin since the Energy Information Administration began publishing estimates, with a 12.8 percent increase in 2010, the agency said in its latest annual report.
The EIA calculates natural gas and oil reserves based on an entire year's production data and geologic estimates that improve as energy companies drill more holes and form a better picture of what lies beneath.
Six shale plays across the country comprised 96 percent of the nation's proved oil and gas reserves, with Texas's Barnett Shale taking the top spot.
The reserves in the Marcellus tripled from 2009 to 2010, the agency said, as drilling picked up and the region saw the introduction of some major multinational drillers during that time.
Reserves of "wet" natural gas, or gas that comes loaded with hydrocarbons such as ethane and butane, rose by 11.9 percent.
The EIA is currently compiling information for the 2011 report and expects to issue it in 2013. Agency officials said they anticipate dry gas production to fall in 2012 and 2013, owing to low natural gas prices.
The jump in Marcellus production in the EIA report led the industry newsletter Powell Shale Digest to say "it is reasonable to assume" the Appalachian formation will eventually become the top natural gas producer. That title currently belongs to the Haynesville Shale of Arkansas and Louisiana, where gas production was recorded as slipping in the EIA report.