An agitated tank having two 45 degrees pitched blade downward turbines in series and four thin baffles which were narrower than the conventional ones was studied. At higher impeller speeds, a gas and liquid vortex induces the gas above the liquid surface vertically downward into the turbines, which in turn cuts the gas stream into bubbles which then circulate in the liquid. Consequently gas-induction increases the gas utilization ratio as well as simplifying the ancillary equipment otherwise required to recycle the escaped gas. The relationship between tank geometrical factors and the liquid mixing time was also investigated. The experimental variables investigated were the impeller speed, the baffle width, the turbine diameter, the space between two impellers, the liquid level, and the clearance between the lower turbine and the bottom of the tank. The results showed that all but the clearance between the lower turbine and the bottom of the tank had significant effects on the mixing time under normal gas-induction, revealing results in contrast to the conventional agitated tank.