The invention relates to an internal combustion engine which can be operated with at least two fuels that have different knock resistance and which comprises at least one cylinder in which combustion of the fuel takes place cyclically. Said engine is provided with a dosing system for feeding a controlled quantity of fuel to the cylinder in every cycle. The dosing system is designed in such a manner that, when fuels are used that are less resistant to knocking, the quantity of air-fuel mixture supplied is maintained below a threshold quantity at which there is no danger of knocking.