The U.S. coal mining industry vented some 158 billion cubic feet of methane gas into the atmosphere in 2006, according to industry officials.

About 22 percent of U.S. coal mine methane emissions came from surface mines. Yet this is a valuable resource.

"Methane from coal mines is a big, big deal. Until recently, nobody cared what happened to the methane; they vented it," said James Holtkamp, who manages the global climate change practice division of the law firm Holland & Hart.

Not only is methane a relatively clean-burning fuel source, but it's also a potent greenhouse gas. So any effort beyond "usual business" to prevent the release of coal mine methane could qualify for carbon credits.

A market for carbon credits was created with an eye primarily on capturing carbon dioxide, another greenhouse gas. But methane is emerging as another commodity under the carbon credit scenario.

Holtkamp said that over the last two or three years, mine operators have realized that methane has value, either as a source of energy or a potential source of carbon credits because methane is a greenhouse gas.

"It's an environmental issue," Holtkamp said.

In Colorado there is a challenge to a coal mine seeking a permit from the U.S. Forest Service. Holtkamp said environmental groups challenged on basis that the mine would ventilate methane and have an adverse climate impact.

"I expect we'll see more and more of those kinds of challenges," Holtkamp said.

But what it means to Wyoming's existing coal mine and coal-bed methane industries is unclear.

Wyoming's surface coal mines typically drill wells ahead of the pit to pump water out of the coal - a process that also vents some methane. In fact, this is how the coal-bed methane industry emerged in the Powder River Basin.

Holtkamp said companies that produce coal-bed methane in the Powder River Basin don't qualify for carbon credits because it is considered primary gas recovery. In other words, the industry doesn't harness a greenhouse gas that would otherwise be vented into the atmosphere. If they didn't produce coal-bed methane, it would remain underground.

But could the same be said of coal-bed methane wells just ahead of mining operations? These are areas where methane production is marginal - so whether it could be considered something beyond business as usual may be left open for interpretation, Holtkamp said.

If there's a national cap-and-trade law, would surface coal mines be required to count the methane released from normal operations? Holtkamp said these are the types of questions that federal cap-and-trade legislation is forcing the industry to face.

Energy reporter Dustin Bleizeffer can be reached at (307) 577-6069 or dustin.bleizeffer@trib.com.