Abstract: The petroleum exploration indicates the complexity of the oil sources and origins of Palaeogene in eastern part, south slope of Dongying sag. The crude oil is characterized by the multi-source and the far-source in this area. The genetic classification and source identification are based on 61 oil and oil-bearing rock samples from different 45 points. The results show that there are three classes of crude oils in origin. Class-I oil is characterized by low m(Pr)/m(Ph) raito, low maturity and high gammacerane index, reflecting the oil may come from the Es₄^s source rock; Class-Ⅱoil by high m (Pr)/m (Ph) ratio, high maturity and low gammacerane index, showing it may derive from the Es₃^x source rock, while Class-Ⅲ oil by relatively high m(Pr)/m(Ph) ratio, relatively low maturity and extremely high gammacerane index, with high content of tricylic terpane and C₂₉-αααsterane as well as little lighter of δ¹³C value, indicating that there existed a set of source rocks to be recognized here. The study shows that the multi-origin types of crude oil mean that in the ramp of this fault basin, there are multiple oil sources and complex processes of oil-gas migration and accumulation as well as much more oil potentials to be explored in the slope of Dongying sag.

Key words: Dongying sag, crude oil, geochemistry, origin