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Fluid inclusion and organic biomarker data show that there was formerly a hydrocarbon system in the Cambro-Ordovician Laurentian margin rocks of NW Scotland. Oil fluid inclusions occur in stylolitized Eriboll Formation sandstone, in K-feldspar cements with an 40Ar/39Ar age of 415 ± 5.5/5.8 Ma (2σ, analytical precision/full external precision). Organic extracts from Durness Group black limestones yield biomarker ratios characteristic of high thermal maturity. Organic maturation to yield oil probably occurred during orogenic deformation along the Moine Thrust Zone. The recognition of a hydrocarbon system in Scotland adds to a huge hydrocarbon province in Laurentian rocks including North America and Greenland.

Supplementary material: Technical data for Ar-Ar dating are available at