The present study deals with the pressure effects on mass transfer parameters within a bubble reactor operating at pressures up to 5 MPa. The gas-liquid systems are N-2/CO2-aqueous solution of Na2CO3-NaHCO3 and N-2/CO2-aqueous solution of NaOH. A sintered powder plate is used as a gas distributor. Three parameters characterizing the mass transfer are identified and investigated with respect to pressure: the gas-liquid interfacial area a, the volumetric liquid side mass transfer coefficient k(L)a and the volumetric gas side mass transfer coefficient k(G)a. The gas-liquid absorption with chemical reaction is used and the mass transfer parameters are determined by using the model reaction between CO2 and the aqueous solutions of Na2CO3-NaHCO3 and NaOH. For a given gas mass flow rate, the interfacial area 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. Furthermore, the pressure increase results in a decrease of k(G) and k(G)a for a given gas mass flow,rate. The values of the interfacial area, which are obtained from both chemical systems are found to be different. These discrepancies are attributed to the choice of the liquid system in the absorption reaction model. (C) 2003 Elsevier Science Ltd. All rights reserved.