Abstract: Based on the basic characteristics of the source, reservoir and cap rocks, three types of oil-gas reservoir-forming assemblages, called the lower, middle and upper assemblages respectively, as well as two derived, called the lower-middle and the middle-upper assemblages respectively, have been divided in the Chengbei fault-ramp. Different oil-gas reservoir-forming assemblages are of different characteristics. Tectonic activities led to the difference of the strata and sedimentation and to the difference of the source, reservoir and cap rocks from north to south of the fault-ramp. So the lower and the lower-middle oil-gas reservoir-forming assemblages are mainly distributed at adjacent sag areas, i.e., the first and the second step regions. The middle oil-gas reservoir-forming assemblage is mainly distributed in the second and the third step regions. However, the upper and the middle-upper oil-gas reservoir-forming assemblages are distributed in the third step region and in the southern slope area.

Key words: oil-gas reservoir-forming, distribution regularities, Chengbei fault-ramp, Qikou sag