Although there is a need for forecasting the performance of enhanced oil recovery processes involving air injection, the capability to do so is still modest. One of the limitations to such forecasting is the lack of knowledge of the reaction chemistry, which leaves questions as to which or how many reactions are needed, and how to obtain values for the associated rate parameters. A model is presented to describe one of the three major categories of reaction that must be considered when simulating air injection: the heat-induced cracking of oil components. The model is well suited for the numerical simulation of air-injection EOR processes with commercial simulators. It is based on the measured rates of pyrolysis/coking reactions of purified SARA fractions separated from two very different sources: a Lloydminster heavy oil, and a Cold Lake bitumen. Most of the results for the two oils were fairly similar, which suggested that the model might apply readily to a broad range of oils. This paper also outlines a modified SARA analytical procedure that proved to be more reliable for this type of study than conventional methods of SARA analysis.