Rates of gas induction and fractional gas hold-up were measured in a 0.57 m i.d. gas inducing type mechanically agitated contactor. Several designs of the impeller were employed for optimizing the rate of gas induction with respect to power consumption. The effect of blade width blade, angle, blade thickness, blade curvature, number of blades, etc. on gas induction, has been investigated in detail. An optimum design has been proposed. Hysteresis in the gas induction rate and power consumption was observed for a wider impeller projecting out of