1 ) A method of controlling operation of a spark-ignition internal-combustion engine comprising at least one combustion chamber and able to use a single-fuel or a multi-fuel combustion mode with at least one fuel type comprising a high octane number and a low energy density and at least another fuel type comprising a low octane number and a high energy density, a method wherein the energy required for the engine to operate in single-fuel mode is provided either by one or the other of said two fuel types and wherein the energy required for the engine to operate in multi-fuel mode is provided by a combination of the two fuel types, characterized in that, for engine operation in multi-fuel mode, the method consists in: determining the set values of the overall energy density and of the overall octane number resulting from the combination of the fuels, feeding into the combustion chamber said fuels with a proportion intended to reach the set values, evaluating the real values of the overall energy density and/or of the overall octane number of said fuels, in case of a difference between the set values and the real values, in compensating for this difference by varying the proportion of at least one of the fuels so as to obtain the set energy density and/or octane number.