The invention relates to a method for the open-loop control of an internal combustion engine, which is operated with a fuel blend of an initial and at least one second fuel, the internal combustion engine having a fuel metering system, a tank fill-level gauge for determining the tank content and a change in the tank content, a sensor for the detection of the cylinder charge for determining an air mass supplied to the internal combustion engine and at least one exhaust gas probe for determining and controlling the oxygen content in the exhaust gas in a closed-loop. According to the invention, two methods, which are independent from each other, are used for determining the composition of the fuel blend.