In this study, we show how physical models describing hydrocarbon/groundwater interaction can be developed by the noble gases in the hydrocarbon phase and, based on these models, initial crustal radiogenic 4He concentrations in the associated groundwater can be calculated. Considering both in situ 4He production and 4He from an external crustal flux, this allows the 4He age of the groundwater associated with each hydrocarbon reservoir to be derived. We illustrate the strengths and weaknesses of this approach using data from case studies from the San Juan Basin coalbed methane gas field in New Mexico, USA, the Magnus oilfield in the UK North Sea and the Hugoton-Panhandle giant gas field that spans Kansas, Texas and Oklahoma, USA.