a method for recognizing the type of fuel actually used in an internal combustion engine ; the recognition method includes the steps of : sensing the intensity of the vibrations generated by the internal combustion engine within a measurement time window ; determining the value of at least one synthetic index by processing the intensity of the vibrations generated by the internal combustion engine within the measurement time window ; comparing the synthetic index with at least one predetermined comparison quantity ; and recognizing the type of fuel actually used as a function of the comparison of the synthetic index to the comparison quantity ; and forcedly altering , when detecting the intensity of the vibrations , the engine control with respect to the normal standard engine control , so as to enhance the behavioral differences of the different types of fuel that can be used by the internal combustion engine .