Over the past 20 years, gas absorption membrane (GAM) contactors have been evaluated as an alternative to packed columns in carbon dioxide (CO2) capture applications. The success of this technology is highly dependent on the wetting relationship between the membrane and liquid solvent used in the system. This paper tests the performance of microporous polypropylene (PP) and polytetrafluoroethylene (PTFE) hollow fiber membranes in a GAM system using aqueous solutions of monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP). Experimental results showed that PP membranes suffer a loss in performance over time when used with aqueous alkanolamine solutions, while PTFE membranes maintain their initial level of performance. A new GAM module design allowed for the connection of modules in series, intermediate data sampling points, and removable membrane cartridges. Overall, GAM systems were shown to be an effective technology for absorbing CO2 from simulated flue gas streams, but the solvent-membrane relationship is a critical factor that can significantly affect system performance.