Synthetic natural gas (SNG), also sometimes called syngas or substitute natural gas, is natural gas that is created from materials that contain carbon including biomass, coal, and municipal waste as opposed to the more common method of producing the natural gas from underground reservoirs. Syngas is created by the chemical processes applied to materials containing carbon.
Examples of processes used include anaerobic digestion, gasification, methanation, or pyrolysis of materials containing carbon. When renewable sources of base materials are used, the gas is renewable natural gas (RNG).