The fluid dynamic and mixing characteristics of a new hydrofoil impeller (termed Narcissus) for gas-liquid mixing are reported. This impeller provides significant energy-savings in bioreactor applications. Dye-tracer visualization and CFD simulation have been used to uncover the prevailing flow patterns and the impeller liquid flow map is identified. Flow regime boundaries are shifted from those for disc-style turbines. A mixing time corresponding to the turbulent mixing regime (i.e., Re > 10(4)) is determined. The power characteristics are measured and compared with experimental data obtained for other impellers. The power number for the turbulent mixing regime for both cylindrical and square vessels was as low as 1. The aeration power at moderate Froude numbers (i.e., Fr < 1) decreased typically by only between 10 and 30%, confirming good gas-handling capabilities for the new geometry. The gas hold-up at a given power input was greater than for flat-blade disc-style turbines.