The paper highlights how key results from historical exploration for conventional hydrocarbons, dating back over 70 years, led to the discovery of a new shale oil resource play in the UK.Early conventional exploration in the West Lancashire sub-basin, conducted by D'Arcy Exploration, a forerunner of BP, was focussed on areas of surface seepage, and resulted in the discovery of the shallow Formby oilfield in 1939. In the late 1940s and early 1950s, a number of deeper wells were drilled, without success, targeting a proposed large Carboniferous conventional trap, leakage from which was thought to be source of the shallow accumulation.