a method and apparatus are provided for humidifying fuel , and optionally oxidant , supplied to a fuel cell system , which can be a single fuel cell or a multiplicity of fuel cells . a catalytic reactor is provided , which is supplied with a portion of the fuel and the oxidant . the fuel is supplied in excess of the oxidant to the catalytic reactor , so as to generate a stream of fuel which is both heated and humidified . for a closed system , a heated and humidified fuel flow , and optionally a heated and humidified oxidant flow , are mixed with additional flows of these gases supplied to the fuel cell .