This paper describes how the reservoir rock affects the minimum oil content necessary for the self-sustained combustion, which is introduced as a new criterion for the selection of suitable reservoirs for the process. Differential scanning calorimetry (DSC) was used to determine the heat value of the oil in the presence of the reservoir rock. The minimum amount of oil necessary to sustain the combustion was calculated from these two parameters and compared with the oil content of the reservoir. Reservoirs with oil contents greater than or equal to this minimum value were considered feasible.