In this work, the transfer rate of air to water in a sparged agitated pressure vessel was studied. The mass-transfer coefficient of air was proved to depend on the mixing energy per liquid volume (P-g/V), the air flow rate per liquid volume (Q(a)/V) as well as the vessel's pressure and temperature. The derived equation, which correlates these parameters with the mass-transfer coefficient, can be used for the design of a pressure vessel included in a dissolved air flotation process.