According to conventional wisdom, oil generation from kerogen is caused by increasing temperature and time during progressive burial of source rocks in sedimentary basins (Tissot and Welte, 1984). However, this paradigm has come into question in recent years with growing recognition of the likely dependence of kerogen degradation and the maturation of petroleum on the dramatic decrease in oxygen fugacity with increasing depth in these basins. In order to determine which hydrocarbon species are favored by thermodynamics to predominate in kerogen, bitumen, and petroleum with increasing depth of source rock burial, comprehensive Gibbs free energy minimization calculations will be carried out with the aid of computer code EQ3NR (Wolery, 1991) using values ofthe standard molal thermodynamic properties of high molecular weight hydrocarbons computed by Richard and Helgeson (1996), together with those reported by Helgeson et al. (1996) for their lower molecular weight counterparts. The results of these calculations will then be compared with reported compositional data to determine the extent to which they agree with geologic reality.