In this study, the behavior of gas dispersion in a bubbling fluidized bed was investigated. Carbon dioxide was used as the tracer gas. Most of the gas jets from tuyeres are towards the same direction, parallel with the longitudinal axis. The movement of particles in the lateral direction was enhanced by the momentum of horizontal gas jets within the bed. The experimental results show that the effect of superficial gas velocity on the gas mixing depends on the distributor type. Comparing with perforated distributor, a better performance of gas mixing was observed while the bed was equipped with horizontal nozzle distributor. (C) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V All rights reserved.