The absorption behavior of carbon dioxide using a hollow fiber membrane contactor was numerically analyzed. In this analysis, the absorbent solution is flowing in the inner side of the fiber bore and the pure gas in the shell and the module operated in a non-wetted mode. The derived coupled non-linear governing partial differential equations were numerically solved by the orthogonal collocation technique. Three typical alkanolamines of industrial use, the diethanolamine (DEA), the 2-amino-2-methyl-1-propanol (AMP), and the diisopropanolamine (DIPA) were used as absorbents in this work. One important feature of this study was building the mathematical model based on the two-step carbamate formation model instead of the one-step model used by previous investigators. The outlet absorbed dioxide concentration was simulated and studied with respect to the liquid velocity, initial amine concentration and external mass transfer coefficient. The analysis includes the effects of the diameter and length of the fibers on the liquid outlet gas concentration as a function of the liquid velocity in the fiber. Simulation results show that AMP solutions present a much higher absorption capacity compared to the other two amine solutions. (c) 2008 Elsevier Ltd. All rights reserved.