Previous attempts at U-Pb dating of uraniferous bitumens have had limited significance because of radioelement migration. Pb-Pb dating, which can be undertaken regardless of recent lead migration, has been successfully applied to uraniferous solidified bitumen from the Ty Gwyn copper deposit, North Wales. Analyses of five bitumen samples with variable mixtures of radiogenic and common lead yield a 207Pb/206Pb age of 248 ±21 Ma (Early Triassic). This age is interpreted as the date of hydrocarbon migration into the deposit and is reasonably consistent with the timing of hydrocarbon generation calculated from the regional burial history. The Pb-Pb dating method could be applied to date uraniferous bitumens representing hydrocarbon migration in diverse geologic environments.