NOVELTY - A method for preferentially oxidizing carbon monoxide in a gas stream containing carbon monoxide, hydrogen and oxygen, involves: contacting the gas stream with a catalyst comprising a mixture of platinum, copper, and iron.    USE - For preferentially oxidizing carbon monoxide in a gas stream containing carbon monoxide, hydrogen and oxygen (claimed) for use in fuel cells.    ADVANTAGE - The platinum catalyst decreases the magnitude of the concentration of carbon monoxide (CO) made by reverse water gas shift (rWGS), when iron and copper are added to platinum (Pt) catalyst compared to the catalyst containing only copper or iron added to platinum. The rWGS is both kinetically and thermodynamically controlled such that the catalyst containing iron (Fe) and copper (Cu) can be used at both higher temperature and lower space velocity than comparative catalyst (Pt with Cu and no Fe). The combination of iron and copper with platinum results in extending the operational window to lower temperature, this is particularly evident as the operational space velocity increases, the result of this is the ability to operate the catalyst at a temperature that is not possible when only copper is added to a platinum washcoat. The gas stream for the water-gas shift is typically contacted with the catalytic material at a process temperature lower than 200degreesC, often at low or ambient temperature e.g. less than or equal to 125degreesC. The catalyst reduces the amount of CO in the gas stream to not greater than 0.001 mol.% (preferably to less than 3 parts per million (ppm)) and rate of CO conversion was of at least 95 (preferably at least 98)%.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a catalyst as a preferential oxidation catalyst comprising a support impregnated with catalytic metals platinum, copper, and iron, where the platinum is present on the support in an amount of 1 - 5 wt.%, the copper is present on the support in an amount of 2 - 12 wt.%, and the iron is present on the support in an amount of 0.1 - 2 wt.%.