Simple mechanisms are proposed for both NO decomposition and NO2formation at typical combustion conditions. Analytical studies indicate that the fast NO2reactions, NO2+ M NO + O + M and NO + O2O + N2, have a strong effect on both systems. During NO decomposition (1400 < T < 2500°K), these reactions maintain equilibrium between atomic and molecular oxygen. They also promote rapid conversion of NO to NO2(600 < T < 1200°K) in the presence of atomic oxygen, and may thus explain NO2formation in gas turbine combustors. Practical evaluation of both mechanisms will require consideration of hydrocarbon kinetics and mixing effects.