A tank ventilating valve is disposed in a regeneration pipe which connects a storage container collecting fuel gas of a fuel tank to an intake pipe of the internal combustion engine. The tank ventilation system is air tightly sealed towards the atmosphere prevailing outside the motor vehicle while the tank ventilating valve is opened to create a negative pressure in the tank ventilation system. The method has the following steps: determining the fuel gas charge of the storage container; determining the volume flow rate through the tank ventilating valve; calculating an intermediate value from the product of the load and the volume flow rate; determining a tank pressure difference between the pressure prevailing in the fuel tank and the atmospheric pressure; and determining the additive corrective value by adjusting the intermediate value to the amount of the tank pressure difference.