NOVELTY - A fuel cell system (22) is operated by applying oxidant and supply fuel (42) to fuel cell stack (24) used to produce electrical current; detecting level of electrical current produced by the fuel cell stack; determining target proportion of the supply fuel applied to the fuel cell stack that is consumed by the fuel cell stack for a given level of electrical current; and varying the supply pressure to maintain a proportion of supply fuel applied to the fuel cell stack that is consumed by the fuel cell stack at about the target proportion of the supply fuel.    USE - Method for operating fuel cell system (claimed), useful in households, vehicles and other commercial applications where the system is used by individuals that are not trained in the operation of fuel cell systems. It also enables use in environments where technicians, or even other individuals, are not normally present, such as in microwave relay stations, and unmanned transmitters or monitoring equipment.    ADVANTAGE - The method enables the fuel cell system to be implemented in commercial devices where it is impracticable for an individual to be constantly monitoring the operation of the system.    DETAILED DESCRIPTION - Operating a fuel cell system (22) comprises providing supply fuel (42) at supply pressure; applying oxidant and supply fuel to fuel cell stack (24), which has fuel cell, and which is used to produce electrical current; detecting level of electrical current produced by the fuel cell stack; determining target proportion of the supply fuel applied to the fuel cell stack that is consumed by the fuel cell stack for a given level of electrical current; and varying the supply pressure to maintain a proportion of supply fuel applied to the fuel cell stack that is consumed by the fuel cell stack at about the target proportion of the supply fuel.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of a fuel cell system.    Fuel cell system (22)    Fuel cell stack (24)    Supply fuel (42)    Storage device (62)    Fuel processor (64)    Feed stream (68)