Farmers, waste management companies and the energy industries have long experimented with converting methane, a byproduct of decomposing organic matter, into transportation fuel.

Those efforts have met with mixed success, and a renewable natural gas fuel has not been widely available in the United States. But now, one leading supplier of natural gas transport fuel is taking a big step toward changing that.

Clean Energy Fuels will announce on Thursday that it has started selling a fuel made of methane from landfills and other waste sources at its more than 40 filling stations in California. The company, which is backed by T. Boone Pickens, is developing a nationwide network of natural gas pumps and plans to introduce the fuel elsewhere as well.

The company expects to sell 15 million gallons of the fuel in California this year, more than double the amount of similar fuels the Environmental Protection Agency projected would be produced nationwide.