Abstract: Performance of gas bubble column has been investigated.It is found that the velocity of the flow of gas through the orifice, uo, must be greater than a critical value, uoc. Pressure drop accross the orifice-plate and surface energy required for bubble formation are estimated. The equations for calculation of critical velocity, uoc and the maximum openning fraction of gas distributor are proposed. Pulse-tracer technique has been used for determination of residence time distribution (RTD) of liquid in bubble column. A non-integer number of tank-in-series model is suggested, and RTD function has been derived. It is shown that RTD function derived fit well the experimental data. Towells equation is recommended to predict the axial dispersion coefficeint of liquid in gas bubble column.