This paper presents a theoretical study of nitric oxide emissions from an unthrottled stratified charge, spark ignition engine. This investigation was undertaken to determine the nitric oxide production when an ideal rich-lean stratification is present and to determine the effects of introducing an intermediate stoichiometric region. In order to study this problem a three-region (generally rich, stoichiometric, and lean) combustion model was used, and the effects of the following variables were studied: 1.Excess air number of the rich mixture. 2.Percentage of the total fuel in the rich-mixture region. 3.Percentage of fuel burned stoichiometrically. 4.Exhaust gas recirculation, percentage and distribution. Comparisons are made to both experimental results from a throttled engine and calculated results for an unthrottled engine with a homogeneous mixture. For illustrative purposes, an application of the model to a particular geometrical form of charge distribution is analyzed.