General Motors' Shreveport assembly facility has become the company's fourth location to use landfill gas.

Three other GM facilities - an engine plant in Toledo, Ohio, and assembly plants in Michigan and Indiana - also use landfill gas to power plant boilers, and a fifth project is underway at an assembly plant in Oklahoma City.

GM's service parts operations headquarters in Grand Blanc, Michigan also uses landfill gas by purchasing eight million kilowatt-hours of electricity annually, generated from the Granger Energy landfill gas-to-electricity project.

According to the World Resources Institute and the Green Power Market Development Group, GM is the largest non-utility user of landfill gas in the US.

"All of GM's landfill gas projects have proven to save money, generating annual savings greater than $US500,000 at each plant," a spokesman said.

GM has reduced its natural gas consumption 21% since 1995.

Landfill gas is 50% methane and is released from waste as it decomposes in landfills.