Stratigraphic, lithologic, and geochemical data provide ample evidence that carbonate rocks and not shales are the source beds of commercial oil in carbonate grainstone reservoirs of the Lower Cretaceous Sunniland Limestone of the South Florida basin.

Detailed crude-oil-source-rock correlations, including gas-chromatographic-mass-spectrometric analyses of steranes, and of tricyclic and pentacyclic terpanes, indicate that the algal-sapropelic, organic-rich argillaceous limestones in the lower Sunniland Limestone, particularly the downdip, basinal facies, are the probable major source of upper Sunniland oil.

Conventional geochemical maturity parameters, plus biomarker isomerization ratios, indicate that the Sunniland oils and source rocks are marginally mature. The sterane ratios, commonly in conjunction with the extended hopane isomerization ratios, proved invaluable in deciphering the thermal maturity of carbonate rocks in south Florida and in pinpointing the upper threshold of the conventional oil-generation zone.