The effects of impeller blade width and blade number on the gas dispersion behaviour of disc impellers with semicircular blades have been characterised. Increasing blade width or number increases the ungassed turbulent power number and reduces the drop in power draw upon gassing. While speed and power required for gas dispersion decrease with increasing blade width and number, the dispersion torque is relatively independent of these impeller geometric characteristics. A three-blade impeller exhibits the worst gas dispersion characteristics, while a four-blade impeller with non-uniform blade spacing outperforms a four-blade impeller with uniform blade spacing.