The main challenge to predict at Field scale the performance of an air injection process is to understand the oil oxidation process and to have a kinetic model of reactions enabling the prediction of process behavior in a reservoir numerical simulator, under different operating conditions.   Recently, the Isoconversional Principle has been implemented for studying the kinetics of reactions associated with oil oxidation during air injection, based on Ramped Temperature Oxidation tests (RTO). In different published papers, the isoconversional analysis has been used to study the oxidation characteristics of different rock-fluid systems, identify groups of dominant reactions during the crude oil oxidation process, and estimate the effective activation energy for each of the identified reactions.   However, in none of them has a procedure been established for estimating the pre-exponential factor, as this is not a direct measure of isoconversional methods. In this article, a mathematical procedure is proposed for estimating the pre-exponential factor based on the application of Friedman's isoconversional method, inteded for characterizing the kinetics of the reactions associated with the In Situ Combustion process.  This procedure was validated with experimental information and a kinetic model proposed in the literature to model the oxidation behavior of heavy crude.