Studies of the physical and combustion properties of saturated hydrocarbon gaseous fuels have shown that there is a remarkable correlation between these properties and the hydrogen to carbon ratio of the fuel molecules. If the correlation is limited to the four most prevalent constituents of natural gas fuels, i.e., methane (CH4), ethane (C2 H6), propane (C3H8) and butane (C4H10), it appears that the flow and combustion characteristics of the pure gases and mixtures of these same gases can be predicted from the H/C ratio alone, independent of the various proportions of the gases. It was concluded that if the H/C ratio of a mixture of gases could be determined by means of an on-line dynamic sensor, important engine and fuel management parameters, such as octane no., methane no., density, stoichiometric air/fuel ratio, etc. could be determined and compensated for by an electronic control unit. Such a sensor has been designed, demonstrated and used as an input to an electronic engine control unit. The software of the electronic control unit of a fuel management system can make adjustments to instantly compensate for variations in fuel composition and quality.