Data gathered from 30 large domestic natural gas producers indicate that the U.S. inventory of gas reserves has grown to about 300 Tcf, according to a new report from the American Gas Association (AGA). That estimate, based in large part on new discoveries in shale plays, shatters the previous domestic reserves record of 293 Tcf, which was recorded in 1967.

“This ‘on-the-shelf’ inventory is the foundation, along with growing national resource estimates, that may point to as much as a 100-year natural gas supply in America,” said AGA CEO Dave McCurdy. “This abundance is helping to reduce prices and increase stability for our customers and also ensuring that natural gas is America’s domestic, clean foundation fuel for now and into the future.”

In its “Preliminary Findings Concerning 2011 Natural Gas Reserves,” AGA defines natural gas reserves as those quantities of natural gas estimated to exist as the result of drilling and completion of existing wells.

AGA’s tally differs from that of The Potential Gas Committee (PGC), which last year estimated that the United States had ended 2010 with 1,898 Tcf of natural gas in the ground (see Shale Daily, April 28, 2011). PGC uses a broader definition of all natural gas in-place that may be considered as future supply, including gas yet to be discovered, according to AGA.

“When periodic assessments of undiscovered resources are combined with proved reserves a vision of future supply of natural gas emerges. Today, the combination of reserves information and resource assessments places that future supply at 2,100 Tcf or greater,” AGA said. “That represents about 100 years of supply at current gas production rates, which are 22-23 Tcf per year.”

The 30 large reserve holders referenced in the report account for about 54% of domestic reserves and about half of U.S. production. “If the thousands of smaller producers that account for the other half of U.S. natural gas reserves and production reached similar results during 2010 and 2011, then growth in domestic reserves and production has been assured,” AGA said.

The United States currently consumes about 24 Tcf of natural gas annually, according to AGA.

“New discoveries tied to investment in onshore drilling opportunities in the Lower 48 states, specifically shale gas, have been a significant factor in recent increases in reserves,” AGA said. “Sustaining the national reserves inventory is a prerequisite for sustaining or growing natural gas production, which is necessary to support future long-term market demand and currently provides more than 90% of the natural gas consumed in our nation.”

The Energy Information Administration (EIA) did not publish reserves volumes for natural gas, natural gas liquids and oil last year due to budget constraints. In its 2010 report, EIA estimated that U.S. natural gas proved reserves, including natural gas liquids, increased by 11% in 2009 to 284 Tcf — the highest level since 1971, with shale gas plays leading the charge (see Shale Daily, Dec. 1, 2010).

ExxonMobil Corp. is now the largest gas reserves holder in the United States, with more than 26 Tcf, after it bought XTO Energy Inc. more than two years ago, followed by Chesapeake Energy Corp., BP plc, ConocoPhillips and Devon Energy Corp., according to the AGA report.