1. British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
2. Netherlands Institute of Applied Geoscience TNO — National Geological Survey, Kriekenpitplein 18, PO Box 80015, 3508 TA Utrecht, The Netherlands
3. StatoilHydro Research Centre, Rotvoll, N-7005 Trondheim, Norway