The previously published multistage three-phase model (proposed by El-Halwaghi and El-Rifai) has been improved by considering axial dispersion in the bubble phase. Comparing the predicted results of the developed model with the different experimental data available in the literature showed a close agreement on both axial concentration profile and overall conversions. The presented model is found to be valid over a wider range of operating conditions as compared to the original model. At high reaction rates where the shortcomings of the hydrodynamic model come to light as well as at high superficial gas velocities where the reactant concentration in the bubble side is critical in reactor performances, the developed model gives obviously better results. It has also been shown that the proposed model is attractive in scale-up procedure. The effects of enlargement of bed diameter on reactor performances could be predicted by the presented model more reasonably.