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Extensive magmatic activity took place in the VÖring Basin, o¡shore Norway, related to the Early Cenozoic rifting.The break-up of the North-Atlantic at the Palaeocene^Eocene transition induced strong volcanism.There are numerous magmatic sills below 3 km depth in the area.They are predominantly layer parallel and thin compared with their lateral extent. Igneous intrusions, sills and dykes a¡ected the temperature history, and thus need to be taken into account in petroleum prospect analysis.We have calculated the temperature and maturity e¡ects in the sedimentary layers in the Gjallar area associated with the emplacement of single sill and sill complexes. A 120-m-thick sill produces a theoretical vitrinite re£ectance (%R 0 ) 0.8% higher than normal at a distance of 100 m from the sill.Vitrinite re£ectance changes caused by a swarm of seven sills varying from 8 to 80 m in thickness were calculated. It is shown that the calculated thermal pro¢le can account for the observed shift in vitrinite re£ectance in the well. A two-dimensional section crossing the Gjallar Ridge, consisting of numerous magmatic intrusions, is also modelled.The modelled geological development and temperature history over the pro¢le show that there are signi¢cant maturation e¡ects in the interval under investigation. Based on this work, the sill swarm observed in the area could more than double the fraction of the kerogen that has been transformed to petroleum at the (present) depth of 4 km.

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project was continued and finalized at the University of Bergen with Professor Rolf Mjelde as the supervisor. Throughout the whole project period colleagues from Tectonor have been involved, Dr. Willy Fjeldskaar as the main industrial supervisor and Drs. Ingrid Fjeldskaar Løtveit and Ivar Grunnaleite as co-supervisors. The motivation to carry out the present investigation is essentially due to my employment in Tectonor, an enterprise "providing specialized geological expertise to the petroleum exploration industry" (www.tectonor.com). Through the work for the company I was exposed to a number of geological problems, and it was interesting and educational to experience how challenges, faced by the oil and gas industry, raised questions where no clear answer could be found in the research literature. Among the questions surfacing in this way was if it was possible to predict fairly accurately how magmatic intrusions influences the petroleum potential in a sedimentary basin due to acceleration of the maturation of organic material in areas that otherwise would remain immature.

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