An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass transfer rates (and enhancement factors) for a wide range of processes and conditions, for both film model and penetration model, complex kinetic expressions and equilibrium reactions. With the aid of this method it is demonstrated that reversibility has a substantial effect on the absorption rate. Approximate analytical solutions for the calculation of the mass transfer rates presented in literature are checked for their validity. All approximations are of restricted use and can be applied only for a limited number of reactions and it is desirable to check the approximation with the aid of a numerical solution before it is used for mass transfer calculations. The linearization method of Hikita and Asai (Kagaku Kogaku 11, 823¿830, 1963) cannot be applied generally for reversible reactions and therefore can lead to erroneous results. Experimentally determined absorption rates of H2S and CO2in various aqueous alkanolamine solutions can be predicted satisfactorily for the several mass transfer regimes studied.