The performance of a laboratory-scale membrane contactor was investigated for the case of CO2 absorption into separate aqueous solutions of monoethanolamine (MEA) and methyldiethanolamine (MDEA). The variation in the flux of the CO2 absorption rate with the CO2 partial pressure, liquid CO2 loading, liquid velocity, and temperature was studied individually in an apparatus giving well-defined and controlled experimental conditions. A two-dimensional diffusion-reaction model was developed and used to predict the results of the experiments. Initial and boundary conditions for the concentrations of chemical species were calculated by an equilibrium speciation model based on the solution method given by Astarita et al. (Gas Treating with Chemical Solvents; Wiley: New York, 1983). Corrections for nonideality were introduced by using a salting-out correction and by tuning the model to experimental VLE data. It was found that the diffusion of the ionic reaction products had a significant rate-limiting contribution to the observed fluxes and these diffusivities were regressed from parts of the experimental data.