This paper highlights the importance of operating and design parameters to mass-transfer in CO, absorption in columns with structured packings. The study compares the performance of four stainless steel packings, Gempak 4A, Mellapak 500Y, Mellapak 500X and Optiflow. Mass-transfer efficiency of these packings was determined by carrying out absorption experiments in a pilot-scale absorption unit with aqueous solutions of sodium hydroxide (NaOH) and monoethanolamine (MEA) as test liquid. The overall mass-transfer coefficients (K(G)a(e)) were calculated from experimentally determined gas-phase CO, concentration profiles within the test columns. The results of this study indicate that mass-transfer coefficient of these structured packings tested varies significantly not only with operating parameters such as liquid load, liquid CO, loading and liquid temperature but also with design parameters, i.e. the pattern of packing arrangement and initial liquid distribution.