NOVELTY - Multiple-stage reformer system comprises a primary catalytic reformer for receiving a primary flow of hydrocarbon fuel (14) and a flow of oxygen for producing a primary reformate (20). A secondary catalytic reformer is connected to the primary catalytic reformer for receiving the primary reformate. A fuel receiver is provided for entering a secondary flow of hydrocarbon fuel into the secondary catalytic reformer. The primary reformate and the secondary flow of hydrocarbon fuel are acted upon by the secondary catalytic reformer to produce a secondary reformate (130).    USE - For catalytically converting hydrocarbon fuel into reformate containing molecular hydrogen and carbon monoxide for fueling a stack in a fuel cell system.    ADVANTAGE - The multiple-stage reformer system has increased reforming efficiency while maintaining system operability. It provides fuel cell operating strategy for gaseous and liquid hydrocarbon fuels. The reformer sub-system allows for initial ignition and start-up, heat-up of the fuel cell system, and all fuel cell operation from idle to peak power while providing highest efficiency when needed without damaging delicate components during acceleration, turndown, or shutdown.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) fuel cell system comprising a multiple-stage reformer system for catalytically converting hydrocarbon fuel into reformate containing molecular hydrogen and carbon monoxide for fueling a stack in the fuel cell system;    (2) method for making reformate containing hydrogen and carbon monoxide by partial catalytic oxidation of hydrocarbon fuel, comprising utilizing the above multi-stage reformer system; and    (3) method for operating the multi-stage reformer system.    The multiple-stage reformer system comprises a flow of anode tail gas from a fuel cell stack into the secondary catalytic reformer and a mixer (115) for mixing the primary reformate and the flow of anode tail gas ahead of the secondary catalytic reformer. The primary catalytic reformer is an exothermic adiabatic reformer, and the secondary catalytic reformer is an endothermic heated reformer.    DESCRIPTION OF DRAWING(S) - The figure is a schematic drawing of a two-stage reformer system.    Hydrocarbon fuel (14)    Tail gas recycle (16)    Primary reformate (20)    Mixer (115)    Secondary reformate (130)