Comparisons of saturated hydrocarbon and terpane (m/z=191) distributions for 24 Forest City basin oils demonstrate three geochemically distinct groups. Group 1 oils (n=18) are produced from Middle Ordovician sandstones and limestones, and Silurian-Devonian dolomites in anticlines along the north-northeast south-southwest-trending basin axis close to the Humboldt fault, and from the Vassar and Easton-McClouth complex of fields on its eastern flank. Group 2 oils (n=5) are produced from stratigraphic and combination structural-stratigraphic traps in lenticular Middle and Upper Pennsylvanian sandstones in fields extending south-southwestward from the Kansas City region into the Cherokee platform, and from the Yaege field on the Nemaha uplift to the west of the Humboldt fault. The only group 3 oil is produced from the Kansas City Group in the Davis Ranch field along the axis of the basin.

Rock-Eval and organic carbon analyses of 122 core, sidewall core, cutting and mine samples show good hydrocarbon source-rock potential for intervals from the Middle Ordovician, Upper Devonian-Lower Mississippian, and Middle and Upper Pennsylvanian. Organic matter thermal maturity for all intervals generally increases from north to south. Organic matter in lower Paleozoic strata are generally marginally mature to mature, whereas, organic matter in Pennsylvanian strata are immature to marginally mature. Comparison of saturated hydrocarbon and terpane (m/z=191) distributions from rock extracts with those of the oils show that source rocks for the group 1 oils are shales in the Middle Ordovician Simpson Group; group 2 oils, the Upper Devonian-Lower Mississippian Chattanooga Shale, and group 3 oil, marine black shales within the Middle and Upper Pennsylvanian section.

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