An alcohol sensing device is provided for determining the alcohol content within an alcohol/gasoline fuel mixture provided to an internal combustion engine. The sensing device uses infrared spectrometry measuring techniques. The infrared sensing device determines the ratio of light absorption by the alcohol/gasoline mixture at two discrete wavelengths within the near-infrared spectrum. The two particular wavelengths of interest are preferably chosen so that at one of the infrared wavelengths, alcohol is strongly absorbing while the gasoline exhibits very little absorption, and at the second wavelength both the alcohol and the gasoline exhibit are essentially non-absorbing. A light beam is transmitted through the alcohol/gasoline fuel mixture such that the two discrete wavelengths traverse the same optical path. A first and second detector are adjacently disposed so as to receive the emitted light from each wavelength after their transmission through the alcohol/gasoline fuel mixture. A third and fourth detector are adjacently disposed in proximity to the first and second detectors for sensing the drift in ambient temperatures corresponding to the first and second detectors. Once the signals corresponding to the two wavelengths are obtained and the signals corresponding to the ambient temperatures are factored out, the ratio of the absorbances by the fuel mixture at both wavelengths is computed. From this ratio and the fuel temperature the concentration of alcohol in the fuel is determined.