The sensitivity of our three-dimensional simulator was studied under various operating conditions. It was clarified that, in addition to coal properties, this simulator also has satisfactory sensitivity, with respect to the change in operating conditions. O-2 partition between the lower and upper burners significantly influenced the temperature distribution in a gasifier. Staged gasification not only enhanced carbon conversion and cold gas efficiency, but also led to favorable temperature distribution that suppresses ash slagging in the gasifier. The carbon conversion increased as the O-2/coal ratio increased, whereas the cold gas efficiency reached a maximum value as the O-2/coal ratio increased. The carbon conversion and cold gas efficiency decreased as the load ratio of a gasifier increased, but with a limited magnitude. The predicted results were in good agreement with the experimental data obtained from a 50 ton/day hydrogen-from-coal (HYCOL) pilot-scale gasifier. The results obtained in this research may be useful information for the designing and operation of gasifiers. This simulator can be applied to predict the gasification characteristics of an oxygen-blown HYCOL gasifier.