Coal-gas is the gaseous by-product of the partial combustion of coal to make coke. The liquid by-product produced by this process is known as coal-tar. The gas is a mixture of hydrogen and methane, with small amounts of carbon monoxide and carbon dioxide.

Coal-gas was used as a fuel beginning in the mid/late 1800's, especially for gas lighting before natural gas became widely available in the 1940s. Also known as manufactured gas, it was often called town gas because nearly every town had its' own manufacturing plant.

By-products of this process are of serious environmental concern in both soils and groundwater. Commonly associated with BTEX, Volatile Organic Compounds,aromatic hydrocarbons, metals and cyanide contamination.