United Parcel Service (UPS) will begin using renewable natural gas (RNG) in its fleet of delivery vehicles and tractors after signing a purchasing agreement with Clean Energy Fuels.

The delivery company is working toward driving one billion miles using its alternative fuel and advanced technology fleet by the end of 2017, according to a UPS press release.

Starting this month, UPS will roll out the RNG at stations in Sacramento, Los Angeles and Fresno beginning this month. Between the three stations in California the company estimates 1.5 million gallon equivalents annually of RNG fuel to the 400 UPS CNG vehicles in the state.

Prior to the agreement with Clean Fuels, UPS used RNG to fuel its tractors in the U.K., through its partnership with Mercedes Benz.

"Today's RNG agreement will help mature the market for this promising alternative fuel," said Harrison Clay, Clean Energy's renewables president. "This commitment also positions UPS to use RNG in its extensive natural gas fleet which includes more than 2,500 medium and heavy duty vehicles."