This paper presents the results of gas chromatography-mass spectrometry studies (GCMS-SIM) of 170 oil samples derived from 32 different fields, located in the southern parts of the Pr-Caspian basin for the genetic classification of oils based on their biomarker and aromatic compositions. In addition, 10 representative oil samples from different fields were chosen for carbon isotope analysis of oils, their fractions and individual n-alkanes. The genetic classification based on biomarker distributions revealed different types of oils, distinguishable mainly by lithology of their source rocks: according to their terpane distributions oil samples from Aktube, Dosmukhambetov, S. Nurzhanov, Karasor, Teren-uzek, Akniyaz, Western Prorva and Kisymbai fields were generated in carbonate source rocks, while samples from the rest fields were derived from shaly source rocks. Oils of Karashiganak and Balgimbayev also have a certain contribution of carbonate OM. The results of PCA cluster analysis based on biomarker distributions indicate the presence of genetically different oils in the studied fields. Also it was attempted to determine the direction of hydrocarbon migration pathways between certain objects and horizons.

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