It is a potent greenhouse gas trapping heat in the Earth's atmosphere, but methane can also fuel an incinerator or drive a turbine to produce electricity.

The prospect of using the combustible gas to cut greenhouse gas emissions and produce revenue is drawing interest from entrepreneurs and agricultural companies.

To explore methane's potential, Murphy-Brown, a subsidiary of Smithfield Foods, spent about $120,000 enclosing 20 percent of a 7-acre lagoon on Company Farm 2039 in Sampson County.

"We want to fully understand the potential for energy production from our farms," said Don Butler, director of government relations at Murphy-Brown. "Methane is the one we believe has near-term potential."

Covered animal-waste lagoons are rare in the United States, but prevalent in some countries that limit greenhouse gas emissions. They might become more common in the US if Congress imposes caps on greenhouse gases in the next few years.

That could create a "carbon" economy, giving value to cutting greenhouse gas emissions and creating a market for credits on such reductions.

Last month, American Electric Power, one of the nation's largest power producers, announced the first large-scale program to capture methane from about 200 livestock operations in 11 states from Virginia to Ohio.

Some environmentalists say partially covering lagoons to capture methane treats only one problem, methane emissions. It does not address such issues as odor, ammonia emissions and other pollutants that have long been a problem on factory farms.

"We have a lot of concern about industry taking that route," said Joe Rudek, a senior scientist with the North Carolina office of Environmental Defense, a national advocacy group. "When you collect methane, you're just dealing with the carbon in the waste. The problems come from the other pollutants."

Right now, the captured gas at the Murphy-Brown farm is pumped out when needed to fire an incinerator to cremate two to six dead hogs a week. The rest is burned off, creating carbon dioxide -- a gas that is far less damaging as a greenhouse generator than methane.

Eventually, Butler said, company officials hope to produce electricity from the methane to sell to utilities.

Lawmakers encouraged the concept by approving legislation last week creating a pilot program to generate up to 25 megawatts of power from captured methane on 50 farms -- enough to power about 15,000 homes.

North Carolina is the nation's second-largest hog-producing state with more than 9 million hogs on 2,300 farms, primarily in Eastern North Carolina. Entrepreneurs see opportunity to get in on the carbon economy by using the waste from those farms.

Scott Subler, president of Environmental Credit, a Pennsylvania-based supplier of environmental credits to financial markets, spent several days last week canvassing pork producers in North Carolina. He was looking for farmers willing to let his company install tarps on lagoons.