NOVELTY - A hydrocarbon fuel for a proton exchange membrane fuel cell is reduced by contacting the fuel having sulfur with hydrogen with a hydro-treating catalyst at 300-500degreesF, a total pressure of 50-500 pounds per square inch, and a space velocity of 0.5-10 hour-1 to produce a hydro-treated hydrocarbon fuel; and contacting the fuel with a solid adsorbent or a liquid extractant.    USE - For desulfurizing a hydrocarbon fuel intended for use in a proton exchange membrane fuel cell, in a stationary fuel cell, or a fuel cell used to power a transportation platform (claimed) such as electric vehicle.    ADVANTAGE - The process uses very mild process conditions allowing desulfurization to be carried out as part of an integrated fuel cell system. It allows desulfurization of the fuel at the site of the fuel cell, if stationary, or in the case of a vehicle using an on-board fuel processor, allowing the desulfurized fuel to be fed directly into the fuel cell with minimal opportunity for contamination.    DETAILED DESCRIPTION - Desulfurization of a hydrocarbon fuel for a proton exchange membrane (PEM) fuel cell comprises:    (a) contacting the hydrocarbon fuel containing sulfur with hydrogen in the presence of a hydro-treating catalyst at 300-500degreesF, a total pressure of 50-500 pounds per square inch (psi), and a space velocity of 0.5-10 hour-1 for a time sufficient to convert up to 95% of the thiophenes present in the fuel, to produce a hydro-treated hydrocarbon fuel;    (b) contacting the hydro-treated hydrocarbon fuel with a solid adsorbent or a liquid extractant selected to reduce the sulfur compounds remaining in the hydro-treated hydrocarbon to at most 5.0 ppm;    (c) recovering a hydrocarbon fuel having a reduced sulfur content where it is suitable for use as a fuel in a PEM fuel cell; and    (d) supplying the hydrocarbon fuel recovered as fuel for a PEM fuel cell.    An INDEPENDENT CLAIM is included for a mobile fuel processor for desulfurizing a hydrocarbon fuel as above.