The wetting characteristics of CO2 in rock are of vital importance in carbon geo-storage as they determine fluid dynamics and storage capacities. However, the current literature data has a high uncertainty, which translates into uncertain predictions in terms of containment security and economic project feasibility. We thus measured contact angles for the CO2/water/quartz system at relevant reservoir conditions, and analysed the effects of pressure (0.1 to 20) MPa, temperature (296 to 343) K, surface roughness (56 to 1300) nm, salt type (NaCl, CaCl2, and MgCl2) and brine salinities (0 to 35) wt%. Water contact angles decreased with surface roughness, but increased with pressure, temperature, and brine salinity. Overall the contact angles were significantly increased at storage conditions (similar to 50 degrees) when compared to ambient conditions (always 0 degrees). Consequently quartz is weakly water-wet (not completely water-wet) at storage conditions, and structural and residual trapping capacities are reduced accordingly. (C) 2015 Elsevier Ltd. All rights reserved.