A calculation model has been developed to numerically interpret the simultaneous mass transfer behaviour occurring in the absorption of CO2 and H2S into blended alkanolamines. For this study we have used the amine couple methyldiethanolamine (MDEA) and diethanolamine (DEA). The film and approximate film theories are used to describe the mass transfer phenomena within the liquid phase. The zwitterion reaction mechanism has been used to describe the reaction between CO2 and the alkanolamines, and the Deshmukh-Mather thermodynamic model has been implemented. Reference species for the correction factor used in the approximate film theory are compared The effect of H2S on the absorption of CO2 is studied and the effect of the individual reactions between CO2 and the alkanolamines within the global kinetic scheme is quantified.