Abstract The Bunter Sandstone Formation, UK southern North Sea has previously been identified as having the potential to store a very large amount of CO 2 . Because there are few producing fields in the formation, information about the potential reservoir and seal are sparse, but can be studied from legacy borehole records which were usually targeting deeper horizons. The seal, largely unproven due to a lack of hydrocarbon fields in the area, has been studied to assess effectiveness. The potential of the seal to retain CO 2 , at least where not faulted, appears to be very good. A novel, unit cell technique is used to assess the storage capacity in a multi-well injection scenario, using the ECLIPSE compositional simulation package. After an injection period of 30 years with an injection rate of 1 Mt of CO 2 per year per well, approximately 3.8–7.8 Gt of CO 2 could be stored in the formation depending upon the maximum safe pressure increase. This storage capacity estimate is smaller than a previous estimate, but only by a factor of ca. 0.3–0.5.