U.S. natural gas proved reserves, estimated as wet gas (including natural gas plant liquids) increased by 11% in 2009 to 284 Tcf -- the highest level since 1971 -- according to the U.S. Energy Information Administration (EIA). Shale gas plays led the charge, the agency said.

The increase demonstrates "the growing importance of shale gas in meeting both current and projected energy needs," said Richard Newell, EIA administrator. "Louisiana, Arkansas, Texas, Oklahoma and Pennsylvania were the leading states in adding new proved reserves of shale gas during 2009."

The findings are detailed in U.S. Crude Oil, Natural Gas and Natural Gas Liquids Reserves, 2009, which was released Tuesday.

Louisiana led the nation in additions of natural gas proved reserves with a net increase of 9.2 Tcf (77%), owing primarily to development of the Haynesville Shale. Both Arkansas (Fayetteville Shale) and Pennsylvania (Marcellus Shale) nearly doubled their reserves with net increases of 5.2 Tcf and 3.4 Tcf, respectively. These increases occurred despite a 32% decline in natural gas wellhead prices used to assess economic viability for 2009 reserves as compared to the prices used in reserves reporting for 2008.

"Additions associated with shale gas activity were instrumental in boosting overall wet gas proved reserves," the EIA report said. "Shale gas accounted for more than 90% of total net additions. Key shale states in 2009 include Arkansas (the Fayetteville Shale), Louisiana (the Haynesville), Oklahoma (the Woodford), Pennsylvania (the Marcellus) and Texas (the Barnett and Haynesville/Bossier). The 11% increase in U.S. proved natural gas reserves took place during a low-price environment that resulted in negative revisions to existing reserves.

"This underscores the major improvements in shale gas exploration and production technologies (horizontal drilling coupled with hydraulic fracturing) and efficiencies. Natural gas from shale represented 21% of U.S. gas reserves in 2009, with the majority coming from six major shale areas. The largest shale gas area in the U.S. remains the Barnett in Texas. The only shale of the six to decline in reserves in 2009 was the Antrim Shale of northern Michigan -- a mature, shallow biogenic shale gas play discovered in 1986 that is no longer being developed at the same pace as the other leading shales."

Proved reserves of U.S. oil (crude oil plus condensate) also increased in 2009, rising 9% to 22.3 billion bbl. Texas showed the largest increase in reserve volume, while North Dakota had the second largest increase, reflecting growth in the Bakken Shale. Unlike the situation for natural gas, where proved reserves grew robustly despite lower wellhead prices, the rise in proved reserves of crude oil was supported by a 37% increase in the crude oil prices used to estimate reserves.

EIA's estimates of proved reserves are based on an annual survey of about 1,200 domestic oil and gas well operators.

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