A fuel cell system which has a fuel cell is described. Also provided is a device for producing/preparing the fuel, for example hydrogen, which is connected on its outlet side to a fuel supply line and on its inlet side to a device for supplying fuel. The device for supplying fuel has a dual pump, in which a starting material for the fuel, stored in the motor-fuel tank, and water fed in via a water supply line, which is for example process water produced during the fuel cell process, are mixed to form a fuel/water mixture. This fuel/water mixture is intermediately stored in an intermediate tank before it is fed to the device for producing/preparing the fuel.