Draft-tube fluidized-bed bioreactors for oxygen consuming bioprocesses catalyzed by immobilized cells have been developed. The characteristics of the reactors concerning the intensity of gas-liquid oxygen transfer were investigated by different methods. It was established that the change of volumetric oxygen transfer coefficient and a dimensionless number corresponding to it are in strong correlation with the dissipated power in the reactor. The effect of low density particles modelling cell support on the oxygen transfer was much smaller than it is general in traditional three-phase reactors. It was concluded that the special structural and hydrodynamical properties of the new reactor types can counterbalance the well-known bubble coalescing effect of biocatalyst particles.