Chemical equilibria involving 10 species and adiabatic reaction temperature of methane com-bustion in air under various conditions have been calculated in detail by means of total Gibbs energyminimization of the system. The calculation data show that the adiabatic combustion temperature of CH_4and air at stoichiometric ratio is up to about 2200 K, and the equilibrium concentration of NO is about0.0018, however that of NO_2 is only 1×10~(-6). A large amount of carbon deposition emerges when the CH_4concentration is above 26.5%. The NO and NO_2 appear only when the CH_4 concentration is below 16%.The maximum equilibrium concentrations of NO and NO_2 are 0.0028 and 2×10~(-6) respectively, at about8%CH_4 concentration. The NO and NO_2 concentrations increase with the system temperature at a lowCH_4 concentration. However, both of them can be decreased when CO_2 or steam is introduced into thesystem, which also decreases the adiabatic combustion temperature. The decrease in adiabatic tempera-ture caused by Chemical equilibria involving 10 species and adiabatic reaction temperature of methane com-bustion in air under various conditions have been calculated in detail by means of means of total Gibbs energyminimization of the system. The calculation data show that the adiabatic combustion temperature of CH_4and air at stoichiometric ratio is up to about 2200 K, and the equilibrium concentration of NO is about 0.0018, but that of NO 2 is only 1 × 10 -6. A large amount of carbon deposition emerges when the CH_4concentration is above 26.5%. The NO and NO 2 appears only when the CH 4 concentration is below 16%. The maximum equilibrium concentrations of NO and NO 2 are 0.0028 and 2 × 10 -6 respectively, at about 8% CH 4 concentration. The NO and NO 2 concentrations increase with the system temperature at a low CH_4 concentration. However, both of them can be decreased when CO_2 or steam is introduced into the system, which also decreases the adiabatic combustion temperature. The decrease in adiabatic temp era-ture caused by