Natural gas is considered the cleanest burning and most reliable fossil fuel, but it still isn't a clean energy resource. However, there is an alternative called renewable natural gas (RNG). RNG also goes by the name of biomethane and is produced from livestock, landfill waste, and other organic materials through anaerobic digestion. While it's not a fossil fuel, RNG is completely identical to conventional natural gas in chemical make-up, allowing them to use the same distribution system.