Abstract: The exchangeability of gaseous fuel for a gas turbine combustor was investigated experimentallyand analysed in terms of indices JH and Jj given in ref. (3).Experimental results show that the effects of the alternative fuel componenets on the combustorexit temperature profile and distribution factor are not significant. It is also found that the ratio of H/C affects the combustion efficiency quite notably provided the inlet air-flowis at nomal pressure and temperature, but this effect weakens when the pressure and temperature of the inlet airflow rise.A conclusion is made that the index Jj can be adopted to predict gaseous fuel combustionefficiency and thereby the exchangeability can be evaluated.