Immature oil has been found in a number of Tertiary basins in China.The authors studied the core profiles of the Dongpu Depression in Henan Pro-vince and made thermo-degradation experiment on immature source rocks. Itis found that after hopenes

ββ-hopanes and rear rangment sterenes disappeared successively with the increase of buried depth

the configuration of homo-hopanes came to reach equilibrium. Thermal simulation experiment has pro-ved that lower matured crude oil might be generated from some kinds ofsource rocks during diagenetic stage. The tricyclic terpanes generated in thisstage had the tendency to concentrate in crude oil. The abundance ratio oflower-molecular-weight tricyclic terpanes to higher ones can be used to sub-divide diagenesis.