The pre-Rhaetian Triassic sequence in the Hllviken Halfgraben contains several sandstone layers, which have been investigated concerning their potential as geothermal aquifers. Two geothermal projects managed by E.ON Sverige AB, DONG (Danish Oil and Natural Gas) and HGS (Hovedstadens Geotermiske Samarbejde) resulted in the early 2000s in the completion of four deep wells in Copenhagen and Malm. The wells penetrate an up to 700 m thick pre-Rhaetian Triassic sequence at depths between 1800 m and 2650 m. The geological information from these wells and data from 15 older wells and one cored borehole constitute the main database in this study. The incentive has been the need for a comprehensive characterization of the Triassic aquifers regarding their distribution, lateral extension and petrophysical properties as to assess their geothermal potential on a regional scale.