In the gas industry, the value of natural gases are based on their gross heating values (gross calorific values). Other properties that are important for calculating the amount of gas on a volumetric scale are the relative density (specific gravity) and the compressibility factor. The gross heating value is difficult to measure accurately for a flowing stream whereas the analysis of the composition of the stream by gas chromatography can be done accurately by well established techniques. Thus it is possible to replace a direct calorimetric measurement by a composition determination and a knowledge of the gross heating values of the various components of the gas. We have recently made new recommendations for determining the heating values and the specific gravity of selected components of natural gas based on a re-evaluation of the available experimental data. The method for calculating the gross heating value from these recommended values will be outlined. This calculation method is applicable to all common types of gaseous fuels including dry natural gas, reformed gas, propane—air, carbureted water gas, and retort coal gas provided suitable methods of analysis for all the components of the gas are available.