Hydrocarbon accumulations contain rare gases derived from the atmosphere, the crust and, in some cases, the mantle. The distinctive isotopic structure of these different rare gas components allows them to be resolved. The relative abundances of the He, Ne and Ar in the crustal, mantle and atmosphere-derived components provides information on the physical processes which have operated in the subsurface. When combined with mass balance considerations, which place constraints on the scale of fluid movements in sedimentary basins, the rare gases provide powerful constraints on fluid provenance and transport. Results of case studies from two extensional basin systems, the Pannonian and Vienna basin, and the sub-Alpine loading basin of the Po, illustrate how the rare gases provide information about the extent of hydrocarbon-groundwater interaction, constrain the mechanism of hydrocarbon gas transport, and provide an insight into the behaviour of the fluid regimes in different types of sedimentary basin. © 1994 The Geological Society.
