Abstract New seismic mapping of Skagerrak reveals eight structural provinces. In particular, the Skagerrak Graben appears to be the continuation of the Oslo Graben. The Skagerrak Graben is defined by two major Late Paleozoic faults trending northeast-southwest connecting with the faults bounding the Oslo Graben. Extensive rotated block faulting is observed within the graben and a thickness of more than 2 s TWT of Lower Paleozoic sediments has been preserved. Along the boundary faults sediments of probable Late Paleozoic age have been deposited as erosional products from the fault scarps and a central uplifted area. A substantial part of these sediments may have a volcaniclastic origin. The Skagerrak Graben continues to the north as a province of igneous rocks exposed at the sea floor with Precambrian basement on either side. The Skagerrak Graben is flanked by small half grabens containing probable Early Paleozoic sediments indicating that a wider area was involved in the rift process. The formation of the Skagerrak Graben is related to the dextral strike-slip movements along the Sorgenfrei-Tornquist Zone in Late Paleozoic time. The Kimmerian extensional movements along this zone indicate, however, a decoupling of the Skagerrak Graben at this time. Only minor inversion in the southwestern part of the Skagerrak Graben reflects the major inversion tectonism along the Sorgenfrei-Tornquist Zone in Late Cretaceous-Early Tertiary times.