AbstractThe performance of turbine impellers has been investigated by conventional sulphite oxidation technique in a 5‐litre vessel in sparged gas‐liquid and gas‐liquid‐solid systems. Performance may be limited by flooding of the impeller and slipping and by a third effect for which the term ‘overloading’ is proposed. This is associated with the attainment of a minimum bubble‐size for an impeller operating in a given environment. For a given diameter and speed of impeller this effect will only be observed if the blade height and width exceed certain critical values. Blade areas larger than that required to give the critical blade height and width result in an increase in power uptake without a corresponding increase in gas solution rate. For a given gas flow‐rate and impeller speed, oxygen uptake rates can be correlated in terms of power consumed by the impeller, irrespective of blade shape. The performance of a given impeller is dependent on its speed of rotation, gas flow‐rate and concentration of solids in suspension.