A gold based catalyst was formulated for use as a three-way catalyst in gasoline and diesel applications. The catalyst was comprised of gold supported on cobalt oxide, which acted as promoter. The gold-cobalt oxide clusters had particle sizes of approximately 40-140 nm, and were supported on a mechanical mixture of zirconia-stabilised ceria, zirconia and titania. Under gasoline conditions at sub-stoichiometric and super-stoichiometric oxygen concentrations, fresh catalysts displayed a hydrocarbon T-50 of 240degreesC, a CO T-50 of 85degreesC and a NOx T-50 of 310degreesC. After testing at temperatures of 500degreesC over periods of up to 157 h, the activity of the catalyst decreased.