A modified thermodynamic equilibrium model has been developed to improve the prediction of syngas composition produced by the gasification of woody biomass. A comparison of data produced by an equilibrium model with available experimental data from bubbling biomass fluidised bed gasifiers indicates that the equilibrium model significantly underestimates the methane yield. In the proposed model, a semi-empirical devolatilisation model is used to eliminate the methane deviation by taking into account the fact that methane, which is initially generated in the devolatilisation process, does not reform through gasification reactions. The modified model estimates the syngas composition more accurately than previously published modified equilibrium models.