Experience of developing saline aquifers as CO2 storage sites is limited. Drawing on the experience of hydrocarbon exploration, there are geological risks that may be encountered during the search for CO2 storage sites, such as finding a reservoir of insufficient thickness, of low porosity or lacking an adequate seal. We use drilling records of 382 hydrocarbon boreholes on the UK Continental Shelf to analyse the geological risks of exploring for a new CO2 storage reservoir, on the assumption that the probability of occurrence of geological risks are similar. The most significant risks for a new borehole are the absence of the target reservoir (19 ± 3% of cases), low reservoir quality (16 ± 5%) and lack of trap (16 ± 3%). Overall, 49 ± 8% of subsurface structures, identified from seismic data, can potentially store CO2. For saline aquifers that have already been penetrated by wells within the potential storage site, most of the geological risks are eliminated or at least reduced; reservoir compartmentalization is the major remaining geological risk. This study demonstrates a method to quantitatively apply drilling data from hydrocarbon exploration to the exploration for CO2 storage reservoirs in analogous geological settings.