An exhaust carbon monoxide (CO) emissions model has been developed. This model uses the fuel properties oxygen content, sulfur content, RVP, olefin content, distillation parameters E200 and E300, and aromatic content to predict exhaust CO emissions. This predictive model is based on emissions measured under summer conditions. The model was developed using the same statistical techniques used to develop the exhaust VOC and NOx models (Complex Model) presented in the Environmental Protection Agency's (EPA) regulations for the final rule on reformulated gasoline. It is the objective in this work to briefly outline the procedure used to develop the exhaust CO model, to look at the behavior of the developed model, to examine the predictability of the developed model and to state the limitations of the model.