In this research, thermal characteristics and combustion kinetics of three crude oils (13-27 degrees API) were investigated using DuPont 9900 thermal analysis system (TG/DTG). A sample size of 10 mg. heating rate of 10 degreesC min(-1) were used in the temperature range of 20-700 degreesC under air atmosphere. Theoretically, combustion of fuel can be initiated whenever oxygen comes in contact with fuel. However, the temperature, composition of fuel and oxygen supply dictates the nature of this reaction. In combustion with air, three distinct reaction regions were identified in all crude oils studied known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). A computer program was developed for automatically processing the data to estimate the reaction parameters using different models and the results are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.