NOVELTY - The power system consists of a fuel cell stack having an anode (12) and a cathode (14) separated by an electrolyte (16): electrical energy is produced when hydrogen-containing fuel (18) is fed to the anode and oxygen-containing gas (20) is fed to the cathode. Part of the power is used, when the system is running, to drive a compressor (24) which supplies air or oxygen to the cell stack: a pressurized storage system (28) is used to supply the gas when the cell stack is not operating, until sufficient power is produced to drive the compressor. A valve (32) is used to select the gas source, depending on the power available from the cell stack. Part of the compressor output may be used to recharge the gas storage system when the fuel cell is operating normally.    USE - For startup of a fuel cell power system, especially in connection with vehicle power systems.    ADVANTAGE - Gives simple, rapid startup of the fuel cell system without relying on the normal vehicle battery system, but does not require a special high-voltage battery.    DETAILED DESCRIPTION - The fuel cell stack may be a proton exchange membrane, and one or more pressure vessels may be used for gas storage. The compressed air may be filtered (25) before being sent to the storage system, using a perfluorocopolymer filter: this is used to increase the oxygen content of the air passing to storage. A motor controller (34) may be used to control the power supplied to the compressor motor, with a system controller (30) to monitor the power available from the fuel cell stack and determine the optimum time to change over to compressor operation. The valve may be used to select any combination of gas supply, from 0-100% gas storage or compressor. An ADDITIONAL CLAIM is included, for a method of starting a fuel cell power system using a pressurized gas supply. A computer may be used to calculate the amount of stored gas needed to maintain a predetermined threshold level of power produced by the fuel cell stack: this level is the amount of power required to run the compressor sufficiently to supply compressed air to the cell stack.    DESCRIPTION OF DRAWING(S) - The drawing is a simplified flow diagram of the fuel cell power system.    Anode (12)    cathode (14)    electrolyte (16)    fuel (18)    compressed air or oxygen (20)    air compressor (24)    air filter (25)    gas storage system (28)    system controller (30)    control valve (32)    motor controller. (34)