The use of membrane contactors for post-combustion CO2 capture by absorption into a chemical solvent is currently one of the most intensively investigated topics in membrane science. The main (if not the only) target of employing membra:ne contactors for this application is to provide a significant reduction in size of the absorption unit, as compared to the classical gas-liquid absorption technology, based on packed columns. Surprisingly, this key performance characteristic, which is best expressed through a so-called intensification factor, remains essentially unreported in studies dedicated to CO2 absorption in membrane contactors. In this article, we recall the state of the art in terms of operating conditions and process performance for packed columns applied to CO2 capture. Based on this, a series of challenges for membrane material design and critical process engineering issues are discussed in order to set up a methodology for a better comparison between membrane contactors and packed columns. More specifically, an average volumetric CO2 absorption capacity around 1 mol CO2 m(-3) s(-1) is proposed as a baseline performance of packed columns in order to estimate the intensification factor of membrane contactors. (C) 2012 Elsevier B.V. All rights reserved.