As the state Legislature debates whether to impose a severance tax on helium, a joint venture has plans for a second plant in the Cowboy state.

Matheson Tri-Gas, Inc. and Air Products intend to build and operate a liquid helium plant near Big Piney.

An existing helium plant is operated by ExxonMobil in Sublette County and produces an estimated 25 percent of the world's supply.

Last year, the Wyoming Supreme Court ruled helium produced under a 1920 law is not subject to the state severance tax and the ad valorem tax levied by Sublette County.

During this session, legislators are considering whether to levy a 6 percent tax on helium produced from some federal land.

The Big Piney plant is designed to produce 200 million standard cubic feet per year at start-up. It will process crude helium produced by a natural gas processing facility owned by Cimarex Energy Co. and Riley Ridge LLC. Production is expected to begin in 2009.

Rod De Bruin, manager of the Energy and Water Resources Division, Wyoming State Geological Survey, said the ExxonMobil plant produces natural gas and helium from a huge underground structure called the LaBarge Anticline. The Riley Ridge area is part of the same structure.

Helium makes up about 0.5 percent of the LaBarge plant's gas stream, which is about two-thirds carbon dioxide and 22 percent methane, he said.

In a 1995 article, De Bruin estimated remaining helium resources of 590 billion cubic feet in the LaBarge Anticline, with remaining recoverable resources of about 400 billion cubic feet.

Helium is a light inert gas and the second most common element in the known universe. It is used in a variety of niche applications, including magnetic resonance imaging, blimps, semiconductor manufacturing and analytical chemistry.

Business Editor Tom Mast can be reached at tom.mast@trib.com, or call 307-266-0574.