Abstract: In thisstudy, organicgeochemical characteristics and depositional environments ofthe Tertiary agedoil shales in Beypazarı, Seyitömer, Himmetoğlu, Hatıldağ, Gölpazarı and Bahçecik areas (NW Anatolia)have been examined. The oil shales in all the studied areas have typically high HI and low 01 values. Pyrolysis/TOCanalysis results indicate that while Beypazarı, Himmetoğlu, Gölpazarı and Bahçecik oilshales contain onlyType I kerogen, Seyitömer and Hatıldağ contain dominantly type I but includes minor amounts of Type IIkerogen. Tmax valuesforthese oilshalesindicate that they are all immature.Result ofGCanalyses ofBeypazarı andSeyitömer oilshalesshow only Cl7 and n-alkanes but notshow other n-alkanes. Gas chromatograms ofHimmetoğlu, Hatıldağ, Gölpazarı and Bahçecik shalesshowabimodal distribution dominated with low number n-alkanes. Such a distribution indicates that these shalesare composedpredominantly ofalgea and minor amounts of terrestrial organic matter. Pr/Ph ratios oftheshales suggest that an anoxic depositional environmentfor the Beypazarı, Seyitömer and Hatıldağ shales,and a suboxic environmentforthe Himmetoğlu, Gölpazarı andBahçecikshales deposited.The biomarkerparameters calculated using m/z 217 and m/z 191 mass chromatograms obtained byGC-MS analysis indicate that the oil shales include immature organic matter. Gammacerane, a typicalbiomarkerforsaline depositional environment, has ben determinedfor all oil shales except thosefrom theBeypazarı area. When other biomarker parameters are taken in to account, it is apparent that all shalesdeposited in saline environments. In general, the data gained indicate lacustrine depositional environmentsforthe oilshales in all the studied areas. However, trace amounts ofC}() sterane found in only shalesfrom theSeytiömer area indicate marine input andsuggest lacustrine depositional environment that was occasionallyinundatedby the sea.