The Sivas Tertiary Basin is located on top of the Late Cretaceous Neotethys ophiolitic nappes which were abducted onto both the Pontic belt and the Tauric platform. Organic facies characters of Tertiary units in this basin have been determined by means of total organic carbon (TOC) analysis, rock-eval pyrolysis, vitrinite reflectance data and organic petrography investigation. The total organic carbon content (TOC) of fine grained sediments from the Eocene (Kozluca and Bozbel Formations) are between 0.05 and 2.26% indicating that these formations are poor to moderate in organic matter. Rock-eval analysis yield low hydrogen index (HI) and high oxygen index (OI) values for all samples. The dominant organic matter is type III kerogen and the hydrocarbon-generating potential is thus very low. The vitrinite reflectance (R-o) value is between 0.30 and 0.93%. In the Sivas Tertiary Basin, the Oligocene sediments from the Selimiye Formation are characterized by a low TOC content (0.05-1.72%) and hydrogen index (21-47 mg HC/g TOC). The vitrinite reflectance of Oligocene sediments is 0.38-0.64%. The total organic carbon content (TOC) for Miocene sediments (Hafik and Karacaoren Formation) is 0.07-1.46%. The organic matter content is richer in the Miocene sediments of the Karacaoren Formation marine shelf than in the sediments of the Hafik Formation terrestrial. (C) 1998 Elsevier Science B.V.