A combustion model based on a new approach is proposed and incorporated in a finite-difference code used for predicting temperature and species concentrations in three-dimensional reacting flow systems. The basic premise of the proposed model is that the equilibrium values of temperature and species concentrations can be calculated when initial conditions of pressure, temperature and equivalence ratio are known; and the actual temperature and species concentrations can be estimated by interpolation between initial and equilibrium values if the degree of reaction-ie the extent to which a reaction has proceeded-is also known. The predictions obtained from this model have been compared with those obtained from experiments in a gas-turbine combustor, and also with those predicted by a two-step reaction model. Good agreement with the experimental data has been achieved by the proposed combustion model as regards temperature, CO2 and O2. Furthermore the proposed model has the capacity to predict values of H-2, NO and several other minor species; this was not possible with the two-step reaction model. However, the values of CO are relatively under-predicted near the exit, since the quenching effect has not been taken into account.