The oil of the Lower Jurassic Moonie field, Queensland, is thought by some workers to be derived from underlying marine Permian rocks and by others to be derived from overlying freshwater Lower Jurassic shales. In this study, the detailed distributions of hydrocarbons in the crude oils from the two productive zones of the field are compared with each other and with the distributions in solvent extracts from three samples of a freshwater shale unit which separates the two reservoir sandstones of the field. The C¹³/C¹² ratios of the oils and the sulfur content of the oils, the shales, and the shale extracts also were determined.

The two crudes are very similar except in n-alkane distribution; this difference is attributed tentatively to "separation-migration" as described by Silverman. Two of the shale samples show good correlation with each other, but the third (stratigraphically between the other two) has a higher maximum in the n-alkanes. The difference might be caused by variation in the ratio of land-plant to aquatic material in the organic residues supplied to the sediment.

Comparisons of hydrocarbon distribution between oils and shales show that shale with a hydrocarbon content similar to that of the upper and lower samples could have been the source of the Moonie oils. However, it is not certain how closely these two samples represent most of the Lower Jurassic shales.

Sulfur content of oils, shales, and shale extracts is negligible. The C¹³/C¹² ratios of the two oils are identical and are in the marine range; this fact conflicts with the possibility of derivation from the nonmarine rocks.