Natural gas is a growing portion of transportation fuel consumed in California. While, natural gas has a slight environmental benefit relative to the use of conventional liquid fuels such as gasoline and diesel, the environmental performance of natural gas can be greatly improved by procuring the gas from renewable sources. We estimate the supply curves of producing natural gas from four renewable sources: (1) dairy manure, (2) municipal solid waste, (3) wastewater treatment plants, and (4) landfill gas. We also evaluate how the production of RNG will respond to California's Low Carbon Fuel Policy (LCFS) and compare the welfare impacts of the LCFS policy to an equivalent carbon tax.