Methane-oxygen, methane-nitrous oxide and carbon monoxide-nitrous oxide counterflow diffusion flames have been studied at low pressures. Species concentrations have been measured using probe extraction and gas chromatography, and temperatures have been measured using thermo-couples. Measurements have been compared to predictions of a computer model. The chemical kinetic mechanism input into these models has been found to be successful in predicting essential features of the structures of these flames. However, improvement are still needed to predict some of the structural features of the flames more accurately. For the methane-nitrous oxide flame, rate generation analysis was performed to identify which chemistry is most essential in predicting the methane-nitrous oxide flame structure. The results of this analysis were compared to rate generation analysis of a premixed methane-nitrous oxide flame. The differenoes between these analyses have been noted. The rate generation analysis results can be used to help guide the formulation of chemical kinetic mechanisms of reduced size, which are required by global propellant modelers.