Background: Capillary trapping of gas bubbles and oil blobs within water-saturated media plays an important role for underground gas storage and secondary oil recovery. Wettability and roughness of the surface are elementary properties of a porous medium that determine the trapping efficiency. In previous work [1,2], we demonstrated that glass beads and natural sands display a significant difference (15%) of the trapped gas phase. Here, we carry out a systematic study of the capillary trapping efficiency in dependence of the wettability and surface roughness. Methods: We conducted a series of column experiments to study capillary trapping of gaseous CO2 using both glass beads and natural sands as sediments. Based on the high-resolution non-invasive micro-CT visualization method and subsequent image processing, we quantified capillary trapping efficiency, gas-cluster morphology and gas-cluster size distribution. We used the silanization method for varying degrees of wettability resulting in three different contact angles on microscopic soda lime glass slides: (i) Piranha cleaning (= 7°), (ii) untreated glass (= 30°) and (iii) silanized glass (=100°). Results: We observed that by-pass trapping is the dominant trapping mechanism in glass beads (smooth surfaces). The displacement process is piston-like. For natural sands (rough surface), thick film flow occurs, causing an efficient snap-off trapping mechanism. Our results indicate that the capillary trapping efficiency of natural sands is stronger reduced by a transition from water-wet to CO2-wet 3-phase system (increasing contact angle) when compared to glass beads. [1] H. Geistlinger, I. Ataei-Dadavi, S. Mohammadian, and H.-J. Vogel (2015) The Impact of Pore structure and Surface Roughness on Capillary Trapping for 2D- and 3D-porous media: Comparison with Percolation theory. Special issue: Applications of Percolation theory, Water Resour Res, 51, doi:10.1002/2015WR017852. [2] H. Geistlinger, I. Ataei-Dadavi, and H.-J. Vogel (2016) Impact of Surface Roughness on Capillary Trapping Using 2D-Micromodel Visualization Experiments. Transport in Porous Med., DOI 10.1007/s11242-016-0641-y.