Energy conversion systems based on biomass utilisation are particularly interesting because of their contribution to the limitation of global CO2 emissions; within the possible methods for energy-based biomass utilisation, thermal gasification appears as the most mature technology. In the first design stage, the designer of these systems, or the user looking for performance predictions under different operating conditions, has advantages of running thermochemical simulations allowing a prediction of the syngas composition and calorific value. The equilibrium model described in this paper is very simple, but it considers chemical species typically encountered by biomass gasifiers, and was tested against published experimental data.