CO2 storage capacity increases with CO2 density, which increases with pressure. On the other hand, high pressure also increases the potential of CO2 leakage. Adsorption of CO2 onto pore surfaces of reservoir rocks can increase storage capacity and reduce overpressure, as adsorbed molecules have higher density and occupy smaller space. Previous studies on CO2 adsorption for geological storage focused on shale and coal, which have organic matter to adsorb CO2. However, conventional reservoir rocks sandstone and carbonate can adsorb CO2 as well, although assessing their adsorption capacities is not straightforward.