Criteria to operate kinetic cells used in the characterization of the kinetic parameters for the reactions that take place during in situ combustion (ISC) were defined using computational fluid dynamics (CFD). To evaluate the assumption of complete mixing in kinetic cells, CFD simulations of a ramped temperature oxidation (RTO) test for the Athabasca bitumen were carried out. A dimensionless Damköhler (Da) number was particularly defined for ISC tests and used as an indicator of the homogeneity in the kinetic cell. The simulations were developed using ANSYS Fluent 13.0 by a two-dimensional discretization of the domain and several user defined functions particularly designed for the simulation of ISC. The CFD simulations were compared to a zero-dimensional (0D) model used to represent complete mixing conditions. CFD showed concentration gradients along the kinetic cell axis that were minimized when the operational parameters were modified to obtain Da lower than 7, a value that guaranteed that the behavior in the cell approximated that of complete mixing represented by the 0D model. For Da > 7, dispersion was evident and predictions of the CFD and 0D models were different.