A mathematical model for simulation of gasification processes of solid fuels in atmospheric or pressurised bubbling fluidised beds incorporating bed and freeboard hydrodynamics, fuel drying and de volatilization, and chemical reaction kinetics is presented. The model has been used to simulate four bubbling fluidised bed gasifiers, described in literature, of different scales from atmospheric laboratory scale up to pressurised commercial scale, processing brown coal, peat and sawdust. The gasifiers have been operated within a wide range of parameters using air, air/steam or oxygen/steam as gasification agent, operating with or without recirculation of fines at operating pressures up to 2.5 MPa. The simulation results for overall carbon conversion, temperature and concentrations of gaseous species agree sufficiently well with published experimental data.