An oil flow obtained from the Middle Ordovician Fengfeng Formation Carbonate reservoir in well KG-3 of the Kongxi burial-hill zone in 1993 marked a breakthrough in petroleum exploration of the Lower Palaeozoic strata of North China. The crude oil is considered as being generated from both the Lower member of the Fengfeng Formation and the second Member of the Upper Majiagou Formation in the Middle Ordovician. There are two oil beds to be found too in the Mesozoic sandstone from well KG-4, which is adjacent to well KG-3. For the Mesozoic crude oil from this well, the oil-filling epoch of has been determined to be in the early of the Eocene epoch, and the main source rock has been though as the Carboniferous-Permian Benxi Formation and, in particular, Taiyuan Formation. In this paper 28 samples were analyzed on organic petrology. Acyclic alkanes, cyclic alkanes and 13C fingerprint were used to distinguish between Mesozoic cude oil and Ordovician crude oil. The homogenization temperature (Th) of fluid inclusions and age of illite in the Mesozoic oil reservoir provide evidence for the main source rock and the oil-filling epoch of the Mesozoic crude oil. An oil flow obtained from the Middle Ordovician Fengfeng Formation Carbonate reservoir in well KG-3 of the Kongxi burial-hill zone in 1993 marked a breakthrough in petroleum exploration of the Lower Palaeozoic strata of North China. The crude oil is considered as being generated from both the Lower member of the Fengfeng Formation and the second Member of the Upper Majiagou Formation in the Middle Ordovician. There are two oil beds to be found too in the Mesozoic sandstone from well KG-4, which is adjacent to well KG-3. For the Mesozoic crude oil from this well, the oil-filling epoch of has been determined to be in the early of the Eocene epoch, and the main source rock has been though as the Carboniferous-Permian Benxi Formation and, in particular, Taiyuan Formation . In this paper 28 samples were analyzed on organic petrology. Acyclic alkanes, cyclic alkanes and 13C fingerprint were used to distinguish between Mesozoic cude oil and Ordovician crude oil. The homogenization temperature (Th) of fluid inclusions and age of illite in the Mesozoic oil reservoir provide evidence for the main source rock and the oil-filling epoch of the Mesozoic crude oil.