Calculations of the CO2 storage capacity in the Leman Sandstone Formation and the Bunter Sandstone Formation in the data-rich southern North Sea basin, using structure contour, porosity, and isopach maps and a simulation of CO2 injection, suggest that their CO2 storage capacities are approximately 3 and up to 15 Gt CO2, respectively. It is recognized that such data are not available for most sedimentary basins, and a simple top-down method of calculating CO2 storage capacity would be highly desirable from a policy maker's perspective, so that the storage capacity of a basin, region, or jurisdiction could readily be estimated. Therefore, the above estimates were used to calculate the amount of CO2 stored per unit area and the amount of CO2 stored per unit of pore volume in the Leman Sandstone and Bunter Sandstone formations. The results were compared to similar calculations, derived from published data, for the Utsira Sand, a CO2 storage reservoir in the northern North Sea. The mean CO2 stored per unit area of the formation is 140 kg m−2, and the range is 42–260 kg m−2. The mean CO2 stored per unit pore volume is 6.3 kg m−3, and the range is 1.8–10.0 kg m−3. Two important factors that vary widely between these three North Sea reservoir formations are the total pore volume in traps and the achievable CO2 saturation; neither can be determined without detailed data.