The objective of this study was to investigate the process of generating fuel gas through gasification of biomass in a fluidized bed reactor. The experiments were performed in a pilot scale autothermal gasifier developed in the laboratory. Rice husk having 10% moisture (wb) had been taken as the representative biomass and, air was used as the fluidizing and gasifying media. The work included the parametric study of process parameters such as reactor temperature and equivalence ratio which influence the composition of producer gas. The thermodynamic model was developed based on equilibrium constant approach to predict the fuel gas compositions at different operating conditions. The water gas shift reaction and the methanation reaction were considered to be in thermodynamic equilibrium state in this model. Six major components of the product gas as analyzed in the laboratory were H-2, CO, CO2, CH4, H2O and N-2. It was observed that the concentrations of hydrogen and carbon monoxide were increased with rise in gasification temperature. On the other hand, higher equivalence ratios caused to decrease the concentrations of hydrogen and carbon monoxide, and consequently the heating values of fuel gas. Higher equivalence ratio also resulted in more gas yields due to increase in the exothermic reactions. The model could make a reasonably good prediction for the experimental data as observed for the gas species concentrations. In few cases, particularly for CH4, there were some differences in numerical values of species concentrations and the probable reasons for such deviations have been discussed. (C) 2013 Elsevier Ltd. All rights reserved.