Clean Energy Fuel has announced that sales of its Redeem renewable natural gas more than doubled to 50 million gasoline gallon equivalents in 2015, up from 20 million the year before.

The company said Redeem sales have expanded from Clean Energy public access stations in California and also via contracted customers like UPS, Republic Services, Santa Monica’s Big Blue Bus and the University of California San Diego.

UPS is the largest consumer of Redeem and currently fuels around 400 vehicles in California and as well as portions of its delivery fleet in Texas. In related news, UPS announced it would use up to 500,000 gallon equivalents of renewable liquefied natural gas in Texas. UPS stations in Houston and Mesquite will dispense the fuel to a fleet of about 140 UPS tractors.

“UPS is committed to expanding our use of alternative fuels, including renewable natural gas, to minimize our impact to the environment,” said Mark Wallace, UPS senior VP for global engineering and sustainability. “Renewable natural gas turns naturally occurring methane into an alternative fuel that replaces diesel and its carbon emissions.”

Redeem sales were also expanded to two more states last year, with the renewable fuel now being sold in Oregon and Texas.

Redeem is a renewable natural gas fuel and is also known as biomethane. It is derived from biogenic methane or biogas which is methane that is naturally generated by the decomposition of organic waste. The methane gas is processed, purified and sent into the interstate natural gas pipeline and made available to Clean Energy customers, the company noted.