The fluid flow regime has a great impact on the removal efficiency of oil from wastewater in a dissolved air flotation tank. This study examined the hydrodynamic characteristics of an industrial dissolved air flotation tank by modeling the flow pattern through the residence time distribution curve. The dissolved air flotation tank included an active zone, a plug flow zone and a dead zone. The flow patterns and mixing parameters were experimentally examined throughout the tank by the colored tracer injection method. A mathematical expression predicting the concentration profile of the tracer as it was leaving the system was developed. The simulation results obtained by computational fluid dynamics were compared and found to agree with the experimental results. With the dead zone comprising nearly 22.6% of the tank volume, the results showed that increasing the liquid inlet flow rate increases the mixing zone volume and decreases the dead zone volume. (C) 2012 Elsevier B.V. All rights reserved.