Abstract: Process and apparatus for utilization of fuels with alcohol additives for an internal combustion engine in which during the heating of a sample quantity of a fuel mixture of a conventional fuel and alcohol there is a delay in the temperature increase in the region of the boiling point of the alcohol, due to its heat of vaporization. The apparatus (a) detects this temperature region, which characterizes the type of alcohol in the mixture, and (b) determines the extend of the delay in the temperature increase which characterizes the percent admixture of the alcohol in the fuel mixture. The measurement values obtained during the vaporization are utilized to produce a correction signal in a control device to effect a change in the air-fuel ratio in the fuel mixture former of the internal combustion engine.