This study has compared the power demand of a traditional Rushton turbine with that of three hollow blade dispersing impellers, the Chemineer CD-6 and BT-6 disc turbines and a design based on the ICI Gasfoil. Some of the large gas loadings were achieved by operating in heated water, so augmenting the sparged gas volume with evaporated water vapour. The results show that the power demand in the flooded regime may be significantly higher than in the absence of gas. Furthermore, once flooded, there is a considerable hysteresis that delays the return to loaded operation when the gas rate is reduced, The work has also shown that for a given off-gas rate, the relative power demand of an aerated impeller is almost always greater in a hot system than at ambient temperature, though it is not yet possible to quantify the increase.