Abstract: A system for measuring on-line the energy content and flow of a gas mixture within a pipeline. The system includes a gas chromatograph for producing a time varying signal related to the component composition of the gas mixture. The pressure and temperature of the gas mixture is measured and these signals as well as the time varying signal from the chromatograph are converted to digital form. These signals are applied to control means which produces energy and flow rate signals of the gas mixture in the pipeline based on the on-line pressure, temperature and component composition. These signals are corrected by supercompressibility factor signals as a function of component composition.