NOVELTY - Fuel system includes a fuel cell, hydrogen-rich fuel source, and oxygen-rich fuel source. Humidifiers are placed between the sources and their associated inlets and have a reactive flow path connecting each source and associated inlet with an energy-containing medium flow path and a source of liquid aqueous material for vaporization in the energy-containing medium flow path.    USE - The fuel cell systems have applications, e.g., in automobile installations and where there are volume constraints on the system.    ADVANTAGE - The configuration of the fuel cell system assures the humidification of the reactive streams and minimizes the overall energy consumption of the system.    DETAILED DESCRIPTION - A fuel cell system comprises:    (a) a fuel cell (10) having a hydrogen-rich fuel inlet (14), an oxygen-rich oxidant inlet (12), an anode residual gas outlet (18) and a cathode gas outlet (16);    (b) a hydrogen-rich fuel source (30) connected to the fuel inlet;    (c) an oxygen-rich gas source for the oxidant inlet; and    (d) at least one humidifier (52, 70, 54, 72) between the associated sources and inlets and having a reactive flow path (56, 58, 74, 76) connecting the particular source and associated inlet in a heat-exchange relation with a flow path for the energy containing medium (60, 61, 62, 64, 78, 80, 82, 84) and a source of aqueous material connected to the reactive flow path for introducing the aqueous material to be vaporized within it.    The energy-containing medium flow path is connected to one of the outlets to receive a heated liquid to provide the heat for vaporizing the liquid aqueous material by a heat exchange between the flow paths.    INDEPENDENT CLAIMS are given for variants of the fuel cell system using similar principles.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic representation of a fuel cell system conforming to the invention. (Drawing includes some non-English language text).    Fuel cell (10)    Oxidant inlet (12)    Fuel inlet (14)    Cathode gas outlet (16)    Anode gas outlet (18)    Fuel source (30)    Air humidifiers (52, 54)    Air flow path (56, 58)    Energy-containing medium flow path (60, 61, 62, 64, 78, 80)    Hydrogen humidifiers (70, 72)    Hydrogen flow path (74, 76)