This paper presents a methodology for the determination and measurement of important natural gas combustion properties (Higher heating value, Wobbe index and Stoichiometric Air–fuel ratio). A pseudo-gas formulation is used to determine an equivalent gas composition to the real natural gas tested. The pseudo-composition, made up of the most influent constituents of the natural gas, is determined by solving a system of non-linear equations. The input parameters to the procedure are: the thermal conductivity of the natural gas at 333K and 383K, the speed of sound at 303K and the concentration of CO 2 . A combustion properties measurement sensor has been developed and tested for many natural gas compositions. The tested natural gases are chosen to represent typical European gases as well as to account for large variations of individual components (heavy hydrocarbons, inert gases). With the developed sensor, combustion properties measured at standard conditions agree with gas chromatographic analysis, to within 0.5%.