NOVELTY - Fuel cell system comprises steam reformer for delivery of fuel cell supply stream to fuel cell assembly; jet pump (1) for delivery to steam reformer of gas stream comprising steam and gaseous hydrocarbon fuel; steam generator (6) for delivery of pressurized steam to steam inlet of jet pump; and source of gaseous hydrocarbon fuel for delivery of gaseous hydrocarbon fuel to fuel inlet of jet pump.    USE - Fuel cell system is used for delivering a gaseous fuel, e.g. natural gas or higher (greater than or equal to 2C) hydrocarbons, to a fuel reformer.    ADVANTAGE - Fuel cell system is capable of operating on a main supply of gaseous fuel and does not require the use of a gas booster in order to ensure that the fuel is delivered to a fuel reformer at an appropriate pressure for effective and efficient operation of the reformer. The fuel cell system is economic to construct and operate and has simple control systems to regulate and moderate flow of gaseous species to the reformer.    DETAILED DESCRIPTION - Fuel cell system comprises:    (a) fuel cell assembly;    (b) steam reformer for delivery of a fuel cell supply stream to the fuel cell assembly;    (c) jet pump for delivery to the steam reformer of a gas stream comprising steam and a gaseous hydrocarbon fuel, the jet pump comprising a steam inlet, an inlet for the gaseous hydrocarbon fuel and an outlet for the gas stream;    (d) steam generator for delivery of pressurized steam to the steam inlet of the jet pump; and    (e) a source of a gaseous hydrocarbon fuel for delivery of gaseous hydrocarbon fuel to the fuel inlet of the jet pump.    Flow of steam through the jet pump is responsible for entrainment and flow of gaseous hydrocarbon fuel through the jet pump in order to generate a gas stream comprising steam and gaseous hydrocarbon fuel that is suitable for delivery to the steam reformer. INDEPENDENT CLAIMS are also included for:    (i) a fuel cell sub-system for delivery of a fuel cell supply stream to a fuel cell assembly, comprising a steam reformer for delivery of a fuel cell supply stream to a fuel cell assembly; a jet pump for delivery to the steam reformer of a gas stream comprising steam and a gaseous hydrocarbon fuel, the jet pump comprising a steam inlet, an inlet for the gaseous hydrocarbon fuel and an outlet for the gas stream; and a steam generator for delivery of pressurized steam to the steam inlet of the jet pump, where flow of steam through the jet pump is responsible for entrainment and flow of gaseous hydrocarbon fuel through the jet pump in order to generate a gas stream comprising steam and gaseous hydrocarbon fuel that is suitable for delivery to the steam reformer;    (ii) a method of operating a fuel cell system in which a gas stream comprising steam and a gaseous hydrocarbon fuel is processed in a steam reformer, where flow of steam through a jet pump is responsible for entrainment and flow of gaseous hydrocarbon fuel through the jet pump in order to generate a gas stream comprising steam and gaseous hydrocarbon fuel that is suitable for delivery to the steam reformer; and    (iii) a method of adjusting the steam to carbon ratio in a fuel stream delivered to a steam reformer, comprising entraining a gaseous hydrocarbon fuel and mixing the gaseous fuel with a primary stream of steam by means of a jet pump through a nozzle of which the primary stream passes, where the ratio of gaseous fuel in the mixed flow of primary stream and gaseous fuel delivered to the steam reformer is varied by adjusting the cross-sectional area of the jet pump nozzle thereby adjusting the cross-sectional area of the primary stream.    DESCRIPTION OF DRAWING(S) - The figure shows a jet pump that supplied a steam reformer with a steam/fuel stream via a delivery line.    Jet pump (1)    Delivery line (3)    Steam generator (6)    Mass flow meter (9,13)    Control valve (12)