The use of certain bed materials has been found to increase the steam gasification rate of biomass char. The present work investigates how this phenomenon is influenced by different parameters (e.g., temperature, fuel type, and fuel moisture content), using a laboratory-scale bubbling fluidized bed gasifier. Silica sand, fresh olivine, and activated olivine were employed as bed materials, and three biomass fuels (wood chips, wood pellets, and forest residue pellets) were considered. Switching the bed material from silica sand to activated olivine resulted in a significant increase in the char gasification rate for all three fuels, with further increases noted as the fuel particle size was decreased. The observed effect was strongest (up to 4-fold) during the initial conversion phase (char gasification degrees < 20%) when the temperature was relatively low (≤ 800 °C). The moisture content of the wood chips (0-40%) had no significant effect on the char gasification rate.