The frontal belt of the southeastern Anatolia fold-thrust belt in Turkey contains several small to mid-size oil fields, producing from Cretaceous carbonate of the Mardin Group. Many oil fields are located narrow, asymmetrical anticlinal structures, which are associated with contractional faulting. The Cemberlitas oil field (COF) in Adiyaman, Southeastern Turkey is one of the most important oil fields in the region. The Upper Cretaceous Derdere and Karababa formations of the Mardin Group contain the main reservoir and source rocks in the oil field. We have conducted a detailed study of microfacies, depositional environments and sequence stratigraphy of the Derdere (Cenomanian Turonian) and Karababa (Coniacian Lower Campanian) formations in the oil field. We have recognized 8 microfacies in the Derdere and Karababa Formations in the study area; (1) fine crystalline dolomite, (2) medium-coarse crystalline dolomite, (3) bioclastic wackestone/packstone, (4) lime mudstone (5) phosphatic-glauconitic planktonic wackestone, 6) planktonic foraminiferous wackestone/packstone, (7) dolomitic planktonic wackestone, and (8) mollusk-echinoid wackestone/packstone. These microfacies suggest that the Derdere Formation was deposited in lagoonal to shelf depositional environments. The microfacies also suggest that Karababa Formation was deposited in a deep to shallow marine intra shelf basin. We have identified two-third-order sequence boundaries in the reservoir. These boundaries are of late Turonian and early Campanian age. Each sequence contains transgressive and highstand systems tracts. These sequences are compared with those in other regions to differentiate the local, regional and global factors that controlled sedimentation within the study area.