An experimental investigation of flow between the shrouds of an impeller has shown that gross flow separation can occur for "well designed" shapes. Rotation of the shrouds inhibits separation and if the flow coefficient \nis sufficiently low it will be completely prevented. \n \nFor the particular impeller shroud profile studied it was found that the velocity distribution in the inlet regions (near where the impeller inlet edge would be placed) is satisfactorily approximated by potential theory. \nPotential flow velocity distributions on several families of shroud shapes suitable for impeller or supercharger design are then given for use in design.