The aim of this study is to understand the reasons for instability in the operation of a gas inducing impeller and to suggest the ways to eliminate the instability. Experiments were performed in a 1 m diameter vessel. The impeller clearance from the tank bottom was 0.52 m. The effects of impeller diameter, impeller blade width, blade thickness, impeller blade angle, shape of the impeller blade, impeller position with respect to the stator, impeller submergence and stator geometry on the instability were investigated. Phenomenological description has been provided for the occurrence of instability. An optimum design of a stator-impeller combination has been proposed for gas dispersion and stable operation.