Abstract: Through analysis and correlation of conventional physical and geochemical proper- ties of oils from Santai and North Santai, the authors believe that the properties of the oils are controlled by tectonization within this area, and that heavy oil in the southern slope of Santai and North Santai resulted from the secondary alternation, such as oxidation and biodegradation, occurring in the reservoirs. A Isothrough discussion of source matter and environment, it is shown that those oils are characterized by having similar source environment and deriving from mixed organic matter of Lacustrine facies, with the exception of oil from the northern part (well Bei 16 area) of North Santai, which source organic matter contains relatively high content of lower organisms, and oil from Juarassic of well Bei 27 in the southwestern slope of North Saniai, which is characterized by the slightly oxidizing to reducing source environment and deriving from humic organic matter of lacustrine and swamp facies. The thermal Evolution histories of the source beds indicate that Permian in the foredeep and Permian and Jurassic in the Fukang depression are probably the major source of oils from Santai and North Santai.