An independently-driven, dual impeller system in a transparent vessel of diameter 0.75 m and a liquid height with an aspect ratio of 2 has been studied, with and without a draft tube installed. A Rushton turbine and a Scaba 3SHP1 axial flow impeller were employed with water as the fluid. The power drawn by each impeller was measured independently, both under unaerated and aerated conditions. The hold-up was also measured and both parameters are related to the observed hydrodynamics of the two-phase flow associated with each combination of impellers. Overall, the dual impeller combination with the two being driven at different speeds in the presence of the draft tube, gave the most stable operating conditions and the highest hold-up when compared at equivalent aeration and energy dissipation rates.