A comprehensive process model is developed for biomass gasification in an atmospheric fluidized bed gasifier using the ASPEN PLUS simulator. The proposed model addresses both hydrodynamic parameters and reaction kinetic modeling. Governing hydrodynamic equations for a bubbling bed and kinetic expressions for the char combustion are adopted from the literature. Four ASPEN PLUS reactor models and external FORTRAN subroutines for hydrodynamics and kinetics nested in ASPEN PLUS simulate the gasification process. Different sets of operating conditions for a lab-scale pine gasifier are used to demonstrate validation of the model. Temperature increases the production of hydrogen and enhances carbon conversion efficiency. Equivalence ratio is directly proportional to carbon dioxide production and carbon conversion efficiency. increasing steam-to-biomass ratio increases hydrogen and carbon monoxide production and decreases carbon dioxide and carbon conversion efficiency. Particle average size in the range of 0.25-0.75 mm does not seem to contribute significantly to the composition of product gases. (C) 2008 Elsevier Ltd. All rights reserved.