According to a study published earlier this year, biomethane, upgraded biogas produced from decomposing dairy manure, is a possible renewable – and cost-effective – substitute for natural gas, according to Biomethane from Dairy Waste: A Sourcebook for the Production and Use of Renewable Natural Gas in California looks at the most effective technologies for making biomethane. It also sites markets for the natural gas, as well as specific applications. The report claims that all of the natural gas vehicles in the state could be powered by biomethane produced from the manure of about half the cows in California. With 8.5 million cows in the U.S. generating about 30 cubic feet of manure daily, biomethane, is used as fuel, could power a million vehicles, according to the report. Sweden currently runs 2,300 buses on biomethane made at its 20 biomethane production facilities. A move toward biomethane could possibly improve air and water quality, reduce greenhouse emission, and even strengthen rural economies, the report said.