A new technique using a small pressure sensor was developed to measure the pressure distribution on the blade surfaces of a turbine in an aerated vessel. The following points were revealed. 1) When gas cavities were, formed behind the blades, the pressure over the back surface of the blades rose, and the pressure fluctuation was reduced in comparison with ungassed conditions. (2) Most of the reduction in power consumption when gas was sparged into an agitator at a given speed was due to a decrease in form drag of the impeller. (3) The data on pressure on a blade Surface were applicable to the design of a high performance impeller.