Literary information on methods of assessing the interchangeability of combustible gases was analyzed. The interchangeability of combustible gases (generator gas, biogas, biomethane, hydrogen) in a mixture with natural gas according to Dutton's criteria was investigated. It is shown that according to the criterion of soot formation, almost all the investigated mixtures are interchangeable. Calculations based on the index of incomplete combustion showed that in the entire studied range, the indices of the IСF mixtures were <0.48. According to the flame separation index, the burner will work most reliably on a mixture of biogas and natural gas and biomethane and natural gas. If the content of generator gas in a mixture with natural gas is 50% or more, the flame may break off from the burner.