NOVELTY - An autothermal reactor includes a pulsating mechanism associated with a first inlet to pulsate a flow of first feed gas stream component into the reactor.    USE - For the generation of hydrogen-containing product gas stream for fuel cells.    ADVANTAGE - The invention provides the highest efficiency and increased concentration of hydrogen in the product gas stream, without a corresponding increase in fuel consumption. It is economical to manufacture, easy to operate, rugged in design, and is simple to maintain. It has a varying hydrogen concentration tuning ability, which increases the overall carbon monoxide tolerance of the fuel cell system. Thus, electrical production capacity and longevity of the fuel cell is increased, while reducing maintenance.    DETAILED DESCRIPTION - An autothermal reactor (10) comprises a reactor vessel (14) having a feed gas stream inlet end and a product gas outlet end. A partial oxidation catalyst (20) is located within the reactor vessel and positioned in the path of the feed gas stream. A steam methane reforming catalyst (22) is located within the reactor vessel and positioned downstream from the partial oxidation catalyst in the path of the feed-gas stream. A first inlet (40) is located at the fuel gas stream inlet end of the reactor vessel for introducing a first feed gas stream component that can be hydrocarbon fuel, oxidant, or steam. A pulsating mechanism (45) is associated with the first inlet to pulsate the flow of the first feed gas stream component into the autothermal reactor.    An INDEPENDENT CLAIM is also included for a method of generating a hydrogen-containing product gas from autothermal reactor comprising pulsatingly introducing a feed gas mixture, passing the feed gas mixture over a partial oxidation catalyst, passing the feed gas mixture over a steam methane reforming catalyst, and removing the hydrogen-containing product gas stream.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of pulsed flow autothermal reforming process apparatus.    Autothermal reactor (10)    Reactor vessel (14)    Partial oxidation catalyst (20)    Steam methane reforming catalyst (22)    First inlet (40)    Pulsating mechanism (45)