In the paper a design approach for a biomass fluidized bed gasifier using the comprehensive simulator for fluidized bed equipment (CSFB) is proposed. Performance parameters such as air factor, feeding point position and bed height are determined looking for a maximum gasifier efficiency and gas heating value and a minimum tar content in the gas. Other parameters optimized by using the CSFB software are the pressure drop, the bubble diameter and the gas velocities in the bed. (C) 2003 Elsevier Ltd. All rights reserved.