This paper focuses on the gas-dispersion characteristics of axial flow impellers. Various impellers are compared : an inclined blade impeller with flat blades, an A315 impeller and a Leeuwrik impeller. The goal is to gain insight in the gas-dispersion properties of such axial flow impellers. Therefore, the effects of impeller position and sparger geometry on flow pattern, power consumption and mass transfer are studied in a vessel 0.444 m in diameter, using liquids of different viscosity. The power consumption is strongly related to the different flow patterns and different types of cavities. Under certain conditions time-dependent, asymmetrical flow patterns can occur. The sparger type influences both the power needed to prevent flooding and the overall mass transfer coefficient k1a. The liquid viscosity does not affect the basic hydrodynamic phenomena in the vessel for viscosities not exceeding 80 mPa s.