A polypropylene hollow fiber membrane contactor was utilized to absorb CO2 from a gas stream into an aqueous solution. Three reagents were studied: monoethanolamine, piperazine, and potassium carbonate. Attention was focused on the possible intrusion of absorbent in the membrane pores, which reduces the solute mass-transfer rate. Membrane/liquid interface was thoroughly characterized. The removal efficiency of the reagents contacted with a CO2/N-2 stream was assessed. It is shown that potassium carbonate and piperazine could be considered interesting candidates for applications in membrane contactors, as they appear more successful than monoethanolamine in ensuring proper and stable conditions at the membrane/liquid/gas interface.