In a coal gasifier, CO2 gasification and H2O gasification occur at the same time. Many researchers have constructed CO2 gasification model and H2O gasification model separately. Only a few models explain the competition between CO2 gasification and H2O gasification. These models are divided into two types according to the properties of the active sites. Some models assume that CO2 gasification and H2O gasification occur at separate active sites, whereas others assume that all of the active sites are shared and are common to both CO2 and H2O gasification. There are some coals whose gasification reaction rates, with CO2 and H2O in coexistence, cannot be described by the conventional models. In this study, a Langmuir-Hinshelwood type gasification model was modified to explain the char gasification by CO2 and H2O. In the proposed model, CO2 gasification and H2O gasification partially share active sites. Coal chars, which were prepared through pyrolysis using a drop tube furnace at ambient pressure and 1673 K, were gasified with CO2 and H2O using a pressurized drop tube furnace (PDTF) and a thermogravimetric analyzer (TGA) at various temperatures. The proposed model was found to describe the gasification reaction rates of the experiments more accurately than the conventional models. (C) 2011 Elsevier Ltd. All rights reserved.