The present distribution of Palaeozoic sediments in the Bornholm area is a consequence of several different tectonic regimes during the Phanerozoic eon. This development may be divided into three main evolutionary phases: A Caledonian to Variscian phase encompassing the Lower Palaeozoic sediments. A syn-rift phase characterized by sedimentation in graben areas and expanding basins. A Post-rift development phase dominated by Late Cretaceous carbonate sedimentation. A key to understanding the hydrocarbon potential of the area is the maturation of the organic matter in the main potential source, the Ordovician Upper Alum Shale. Maturity was mainly achieved during the Silurian to Late Palaeozoic time, and little further maturation took place later. The Upper Alum Shale is accordingly expected to be over-mature in the main part of the study area and mature in the Hano Bay Basin. -from Authors