NOVELTY - The method involves detecting and determining mass flow rate of gas, and controlling the gas mass flow rate in gas mass flow rate-control path to a reference variable according to control algorithm. A fuel control path, an oxidant control path and the gas mass flow rate-control path are provided with respective control algorithms in a control circuit. A control is designed in the control circuit such that gas pressure of fuel e.g. hydrogen, and oxidant e.g. air, are coupled with each other by a coupling control. The gas flow rate is modified without influence of the corresponding gas pressure.    USE - Method for operating a fuel cell system (claimed) in a vehicle.    ADVANTAGE - The control is designed in the control circuit such that gas pressure of fuel e.g. hydrogen, and the oxidant e.g. air, are coupled with each other by the coupling control, and the gas flow rate is modified without influence of corresponding gas pressure, thus rapidly, accurately and couplably regulating fuel pressure and oxidant pressure of the fuel cell, and hence allowing the fuel cell to include accurate constant, preset and pretend pressure differences below each other under all operating requirements in large dynamic operating region. The method allows electrolyte-polymer membranes to be efficiently protected against mechanical deterioration due to larger pressure difference, allows the fuel cell to be efficiently operated by the larger pressure difference for obtaining better efficiency during energy conversion.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a fuel cell system with a control arrangement for controlling a gas pressure value of gaseous fuel and gaseous oxidant in respective guide paths of a fuel cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block representation of a control circuit for coupled regulation of gas pressure of fuel and oxidant and coupled regulation of mass flow rate of the oxidant with a state feedback.    Prefilter matrix (F)    Control matrix (R)    Reference vector (Wlw)    State feedback controller (10)    Control path (12)    Integration element (20)