Twenty nine core samples, extending from the surface to 60 m depth, from the Upper Permian organic-rich Ravnefjeld Formation source rock of East Greenland have been analyzed for detailed light hydrocarbon composition. In addition, complementary organic carbon and Rock-Eval analysis, as well as some mineralogical and permeability analyses were carried out. The objective was partly to determine if the changes in light hydrocarbon composition reflect generation patterns (i.e. small-scale changes in kerogen type and amount) or are controlled primarily by redistribution processes. A second objective was to discuss possible modes by which hydrocarbon redistribution took place. The interval examined in the Ravnefjeld Formation is overmature (1.75% R o). Organic carbon contents (TOC) and hydrogen index values range mostly between 1.0–5.5% and 10–20 mg HC/g TOC respectively. The amount of hydrocarbons present in the examined section represent only a fraction of the total amount generated. Petroleum Expulsion Efficiency (PEE) exceeding 0.99 was calculated. Systematic changes of light hydrocarbon composition with depth indicate that effective redistribution has occurred over wide intervals. In particular, there is good evidence to suggest that there was major loss with chemical fractionation of molecular species by depletion into several zones of fractures and also towards the outcrop surface and that fracture occurrence is the single most important factor in controlling the present day hydrocarbon depth trends. In this paper, a novel scheme is presented for effective and objective comparison of hydrocarbon depth trends. The application of this method to elucidation of the migration mechanisms responsible for fractionation during hydrocarbon loss in the fractured zones is illustrated.