A simple model is developed that predicts thermodynamic equilibrium compositions using the ultimate analysis of coals. Coal is represented as CHxOy. The model is validated with the pure carbon-steam system by comparison with literature. The thermodynamic equilibrium compositions are predicted for three Indian coals and compared on the basis of product gas compositions and gross calorific value. The results show that each coal has different equilibrium compositions at identical set of operating conditions. Coals containing higher H/C give more H2 and CH4. The coals containing higher H/C give higher gross calorific value at relatively higher pressures. Thus, high-pressure gasification like Underground Coal Gasification may have an advantage over other processes in terms of product calorific value. The inclusion of the energy balance equation in the equilibrium model will enable us to predict the adiabatic gasification temperature. The model becomes complex due to this, but the additional benefit is that a set of operating conditions is obtained, while reducing one degree of freedom.