The source rock and reservoir characteristics of the Upper Cretaceous‘ A’ Member of the Karababa Formation (Santonian–Coniacian) and the Karabogaz Formation (Campanian) and their relationships to the crude oils produced from the Ikizce and the Tokaris oil fields, were studied using a variety of organic geochemical methods. The Karabogaz Formation is composed of limestone and chert, while the Karababa-A Member consists of clayey limestones. Both formations constitute important source rocks in the Adiyaman Basin. The crude oils examined in this study were produced from reservoir rocks of the same age in two adjacent oil fields. Biomarker characteristics in source rock samples from the Ikizce-A and Tokaris-A wells show that the Karababa-A Member and the Karabogaz Formation were deposited in reducing environments and are characteristic of carbonate facies. Correlations between the source rocks and the crude oils, based on qualitative and quantitative biomarker distributions, indicate that the oils from the Ikizce and Tokaris fields are mixed oils that were derived from both the Karababa-A Member and the Karabogaz Formation source rocks.