The present study deals with the pressure effects on the hydrodynamic flow and mass transfer within an agitated bubble reactor operated at pressures between 10(5) and 100 x 10(5) Pa. In order to clarify the flow behavior within the reactor, liquid phase residence time distributions (RTD) for different operating pressures and gas velocities ranging between 0.005 m/s and 0.03 m/s are determined experimentally by the tracer method for which a KCl solution is used as a tracer. The result of the analysis of the liquid-phase RTD curves justifies the tank-in-series model flow for the operating pressure range. Good agreement is obtained between theoretical and experimental results assuming the reactor is operating as perfectly mixed. Two parameters characterizing the mass transfer are identified and investigated in respect to pressure: the gas-liquid interfacial area and volumetric liquid-side mass transfer coefficient. The chemical absorption method is used. For a given gas mass flow rate, the interfacial al ea as well as the volumetric liquid mass transfer coefficient decrease with increasing operating pressure. However, for a given pressure, a and k(L)a increase with increasing gas mass flow rates. The mass transfer coefficient k(L) is independent of pressure.