Abstract: A calorimeter and method of obtaining the calorific value of a test gas comprises a pair of constant flow pumps one for supplying air at known volumetric flow and the other for supplying a test gas at known volumetric flow. The known volumetric flow of air is maintained at a level sufficient to provide enough oxygen to fully burn all oxidizable components of the test gas. The air and test gas are mixed and catalytically burned in a heated block and the combustion products are thereafter supplied to an electrochemical oxygen measuring cell which measures the remaining oxygen in the mixture. A circuit arrangement is utilized to obtain a value proportional to the difference between the remaining oxygen and original amount of oxygen which value is proportional to the amount of oxygen utilized and in turn proportional to calorific value of the test gas.