The invention relates to a fuel cell system with at least one fuel cell for electrochemical conversion of two reactants. The fuel cell has two electrode areas, having a first supply line for supplying a first reactant to a first electrode area, and an outlet line, for emission of residual gas from the first electrode area. The residual gas has an electrochemically unconsumed portion of the first reactant, a recirculation element, for feeding the residual gas from the outlet line into the first supply line, and an outlet valve in order to emit the residual gas into an area surrounding the fuel cell system. The invention provides for the fuel cell system to have a monitoring unit in order to control the outlet valve. In particular, the monitoring unit opens the outlet valve when the energy required to feed the residual gas by the recirculation element exceeds an energy potential of the first reactant which is present in the residual gas.