Briefly reports on a study comparing the gross composition of crude oil samples derived from different Permian reservoirs on the Gidgealpa Field. The samples were derived from Gidgealpa 7, drillstem test 8, and Gidgealpa 16, DST 2 (Tirrawarra Sandstone and Toolachee Formation respectively). Interpretation of the gas chromatograms of representative aliphatic fractions after their extraction suggests that both oils may have been generated by the same source rock, but that the Gidgealpa 16 oil is more depleted in volatile constituents, perhaps owing to their loss through a more permeable cap rock overlying the Toolachee reservoir. Bacterial alteration of both oil types appears to be miniscule.