Abstract: A method and an apparatus for determining the calorific value parameter describing the calorific value of a gaseous fuel. The apparatus comprises a test burner with a test combustion chamber. An air ratio sensor is arranged in an exhaust gas duct of the test burner and measures an air ratio signal that corresponds to the air ratio of the exhaust gas. As a function of the received air ratio signal, at least one setting signal is generated for a test supply unit via a test control unit. The setting signal controls the amount and/or the proportion of a gaseous fuel or an oxygen-containing gas that is supplied to the test combustion chamber. A calorific value sensor arrangement is provided in the combustion chamber and has an ionization sensor and, a temperature sensor. The sensor signal of the calorific value sensor is transmitted to a determination unit.