A theoretical analysis of the basic chemical kinetic processes which lead to the formation and partial decomposition of nitric oxide and carbon monoxide has been undertaken. A mathematical model of an Otto cycle engine has been formulated, programmed for the CDC 6600 computer, and used to determine species concentrations and thermodynamic properties at any point in the engine cycle. The validity of this model has been confirmed by the results of an experimental program conducted on a typical multicylinder automotive engine, and data available for a single cylinder CFR engine. In addition, the computerized model was used to describe the chemical and physical processes upon which existing control techniques for nitric oxide are based, and to investigate the potential of a new concept, fuel-rich combustion and secondary air injection, for minimizing nitric oxide and carbon monoxide emissions. A unique concept in controlling undesirable engine emissions, i.e., rich combustion followed by secondary air injection during the engine expansion, was shown to result in significant reductions in nitric oxide and carbon monoxide emissions without incurring an appreciable loss in thermal efficiency as compared to stoichiometric operation.