Osaka Gas Company has applied the correlation between the density and calorific value of natural gas to indirect continuous measurement of calorific value. By developing measuring instruments and employing existing instruments, calorific control of send-out gas and calorific monitoring of process gas have been improved in our plant. (1) Rauter meter: This conventional instrument with its high reproducibility and reliability has been used for calorific control of send-out gas at our Senboku Works. Five years of actual operation have produced satisfactory results.