In this study, the effects of ship motion on the CO2 absorption performance of the offshore columns (i.e., the separation columns installed on offshore floating units) are investigated. Specifically, a pilot scale column with 0.4 m diameter and 4 m packed height is used, and NaOH/air system is implemented to measure the CO2 absorption performance of the column under both vertical and offshore conditions. The experimental results obtained from the vertical conditions are used to validate the mathematical model which can compute the effective surface area of the separation columns. Then, such model is used to produce the reference values for the experimental results obtained from the various offshore conditions, where tilt angle, roll motion conditions, liquid load, gas factor, liquid surface tension and liquid viscosity are used as the design variables. The reduction factor is proposed, which can describe the change in the absorption performance of the offshore columns with respect to the important factors. From our study, the tilt angle was shown to be the most important factor, and the mass transfer efficiency was reduced by 8.4% in average (compared to the value obtained under the vertical condition) when the tilt angle was 6 degrees. It was also shown that the roll motion can enhance the absorption performance of offshore columns under certain operating conditions, and the maximum improvement (6.7%) in the mass transfer efficiency was achieved when the liquid load, roll motion amplitude and period were 14 m(3)/m(2) hr, 8 degrees and 45 s, respectively. (C) 2019 Elsevier Ltd. All rights reserved.