The water-gas shift reaction (WGS) is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:CO(g) + H2O(v) CO2(g) + H2(g)The water-gas shift reaction is an important industrial reaction. It is often used in conjunction with steam reforming of methane or other hydrocarbons, which is important for the production of high purity hydrogen for use in ammonia synthesis. The water-gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. The reaction is slightly exothermic, yielding 41.1 kJ (10 kcal) per mole.This reaction has been used as a CO removal method from the reformate for fuel cell applications.The reverse water gas shift reaction has recently found a possible application in In-Situ Resource Utilization on Mars to provide oxygen for fuel for the Mars Direct mission concept.