Abstract: Reservoir geochemistry theory and methods are applied to classifcation of oil family, study of source rock 's hydrocarbon-gener- ating history and analysis of petroleum migration direction in Jiuxi depression. Study shows that the crude oils from six fields in this de- pression belong to the same oil family which could further be divided into three groups of mature, high mature and low mature oils; the oil threshold depths of source rocks in its three sub-sags (Qingnan, Shibei and Dahongquan) range from4 150 m, 3000 m and 3300 m, re- spectively. The crude physical parameters and carbazole parameters in nitrogenous compounds indicate that the direction of Jiuxi petroleum migration should be from west toward east, ie, Qingxi field- →Yaerxia field-→Laojunmiao field- →Shiyougou field, while Shiy- ouhou and laojunmiao fields also have vertical petroleum migration with directions from botom to top, i.e., from L layer to K layer.

Key words: Jiuxi depression, reservoir, geochemistry, oil family, hydrocarbon generating history, migration, nitrogenous compound