Using molecular beam mass spectrometry, the structure of a rich, premixed, flat flame of H-2 + CO + N2O + Ar (phi = 1.19) has been established at 30 torr. Three different mechanisms have been tested to model the flame, with good agreement between calculated and experimental results. It has been demonstrated that the main reaction consuming N2O is N2O + H --> N-2 + OH, while the dissociation reaction: N2O + M --> N-2 + O + M operates like a branching reaction by generating O atoms. The reaction N2O + H --> NH + NO is the main process producing NO. Two of the mechanisms simulate the concentration profile of NO well. As for the processes CO + OH --> CO2 + H and CO + N2O --> CO2 + N-2, only the first plays a significant role in the conversion of CO.