The role of transport effects in experiments on the gasification reactivity of biomass char, conducted in a 26-mm-diameter bench-scale fluidized bed (FB) reactor, is analyzed. Gasification rates of char were measured at various particle sizes, CO2 partial pressures, temperatures, and initial char batches. A dedicated methodology enables evaluation of the transport effects from gas measurements. The separate contributions of fluid-dynamics, external film, and porous diffusional resistances in a typical FB char gasification test are addressed. An optimal adjustment of the operating conditions of the FB is proposed to reduce mass-transport effects as much as possible. When transport effects cannot be completely eliminated, this work shows how to treat the data to obtain an average reactivity that is useful for reactor simulations.