Athabasca bitumen was subjected to thermal treatment of increasing severity under reducing conditions. The generation as well as the change in relative distributions of different components were followed and the resulting products were compared with other Cretaceous oils that lie in the Western Canada Tar Belt and have different degrees of maturity. Reductive thermal treatments converted the bitumen to materials similar to the more mature Cretaceous oils. The saturated hydrocarbons as well as the dinuclear aromatic fractions were of particular interest and were studied in detail. The generation of isoprenoid hydrocarbons is of significance in this study. The optical activities of the investigated oils and the bitumen products showed interesting analogies. All the evidence obtained from this study indicates that the Athabasca bitumen is an immature material.