At the Sleipner gas field in the North Sea, CO2 has been stripped from the produced natural gas and injected into a sand layer called the Utsira formation. Injection started in October 1996, to date nearly 8 million tonnes of CO2 have been injected without any significant operational problems observed in the capture plant or in the injection well. The Sleipner project is the first commercial application of CO2 storage in deep saline aquifers in the world. To monitor the injected CO2, a separate project called the saline aquifer CO2 storage (SACS) project was established in 1998. As part of the SACS project, 3D seismic surveying has been used to successfully monitor the CO2 in the Utsira formation, an industry first. Repeat seismic surveys have successfully imaged movement of the injected CO2 within the reservoir. Reservoir simulation tools have been successfully adapted to describe the migration of the CO2 in the reservoir. The simulation packages have been calibrated against the repeat seismic surveys and shown themselves to be capable of replicating the position of the CO2 in the reservoir. The possible reactions between minerals within the reservoir sand and the injected CO2 have been studied by laboratory experiments and simulations. The cumulative experiences of the Sleipner and SACS projects will be embodied in a Best Practice Manual to assist other organisations planning CO2 injection projects to take advantage of the learning processes undertaken and to assist in facilitating new projects of this type. (C) 2004 Published by Elsevier Ltd.