The conversions of methane, propane, octane and methanol to hydrogen under conditions pertinent to fuel cell operation have been described quantitatively and examined by a series of computer simulations. Catalytic conversion may be achieved by direct partial oxidation or by a combination of total oxidation and steam reforming. Both systems have been simulated, using conversion data and kinetic equations reported in the literature for various catalyst configurations and hydrocarbons. The results show that, in terms of hydrogen produced per weight of fuel and water carried, direct partial oxidation of propane or oxidation/steam reforming of octane are the best alternatives. The latter possess the ease of operation but coke formation may be more of a problem. Methanol, often suggested as a fuel, is much less efficient. Operation of a vehicle using the catalytic conversion system would require fueling by both hydrocarbon and water.