ABSTRACT: In Sivas basin a sequence, comprising detritic and evaporitic sedim.en.ts, approximately 6000 metres in thickness resting upon, a metamorphic and ophiolitic basement, crops out. In this sequence, the occurrences` of two different formations appropriate for being a hydrocarbon source rock: have been determined.. In the. basin, samples collected from, these units have been analyzed in la.borat.ori.es,, On the basis, of these analysis the. potentials of these formations for creation of petroleum .and natural gas,, have been, searched.