In this study the combustion characteristics of crude oils (Karakus and Beykan) in the presence of a limestone matrix were determined using the thermogravimetry (TG/DTG). Experiments were performed at a heating rate of 10degreesC min(-1), whereas the air flow rate was kept constant at 10 L h(-1) in the temperature range of 20-900degreesC. In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures studied known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The individual activation energies for each reaction region may be attributed to different reaction mechanisms, but they do not give any indication of the contribution of each region to the overall reactivity of the crude oils. Depending on the characteristics, the mean activation energy of samples varied between 50.3 and 55.8 kJ mol(-1).