Abstract: A series of generalized formulae for determining the excess air ratio and combustion efficiency on the basis of gas analysis of combustion products for any kind of liquid, solid or gaseous fuel is provided in this paper. Due to consideration of carbon formation and fuel vapors in the combustor and on the surface of the sampling probe, this method can provide more accurate results. Of cause, a generalized computer program can be easily compiled for any kind of liquid, solid or gaseous fuel on the basis of the formulae presented.