The behaviour of inducted gas from a liquid surface and the power requirements in an agitated tank using a mechanical agitator are studied in order to increase the amount of gas self-induction and the gas retention time for gas absorption. A 45 degrees six-blade downward impeller turbine was utilized in this study. Air and water, air and 40 wt%, 60 wt%, and 80 wt% of glycerin water, and air and 106 cP silicon oil were employed as gas and liquid phases. Variables which were studied included geometrical factors (immersed depth of impeller, baffle width and diameter of impeller) and the physical properties of the liquid (viscosity, density, and surface tension). The correlations for the onset speed of impeller and power consumption after gas induction in the agitated tank are established from our experimental results. The amount of gas self-induction from the liquid surface in the agitated tank increases with increasing impeller diameter and speed and decreases with increasing baffle width, depth of impeller and viscosity of liquid.