This report forms part of the international SACS (Saline Aquifer CO2 Storage) project. The project aims to monitor and predict the behaviour of injected CO2 in the Utsira Sand reservoir at the Sleipner field in the northern North Sea, to assess the regional storage potential of the Utsira reservoir, and to simulate and model likely chemical interactions of CO2 with the host rock. This is the final report of Work Area 1 in SACS, whose aims were to provide a full geological characterisation of the Utsira Sand and its caprock. The report summarises the key findings of the component subtasks of Work Area 1. The report also provides references to the various SACS Technical Reports wherein the full details of the scientific work can be found. The report can be downloaded from http://nora.nerc.ac.uk/511461/.