A structural group contribution method is presented for predicting the flammability characteristics of pure hydrocarbon fluids. The method was used to probe the structural groups that have significant contribution to the overall flammability characteristics and arrive at the sets of groups that can best represent the auto-ignition temperature (AIT), the flash point, and the upper and lower flammability limits of about 500 different substances. The structural groups listed were derived from the Joback definition of group contributions and modified to account for the location of the structural groups in the molecule. The calculated values of the group contributions can predict the said flammability properties of pure components from the knowledge of only the molecular structure. The proposed method is very simple and can predict the flash point and the AIT with average percentage errors of 1.8% and 4.2%, respectively. The upper and lower flammability limits are predicted with average deviations of 1.25 and 0.04 vol%, respectively. The results are further compared to those of other published methods and are shown to be far more accurate. (C) 2003 Elsevier Ltd. All rights reserved.