Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer [coke] with air and gasifying it with steam".[1][2] The caloric yield of the fuel produced by this method is about 10% of the yield from a modern syngas plant. The coke needed to produce water gas also costs significantly more than the precursors for syngas (mainly methane from natural gas), making water gas technology an even less attractive business proposition.