The Jiyang Depression consists of a series of semigraben sags which have received deposits since the Eogene period

the lower uplifts that subsided in the Middle-Late Eogene and the over lapped uplifts of the Neogene period. They compose an important part of Bohai Bay petroleum province. Tens ot oilfield snow have been discovered there. Its petroleum production and reserve are the second biggest in China. Among these fields

big- and medium-sized ones areonly 39.5%

but the geological reserve is greater than 75%

the varieties of oil and gas pools are more than thirty

and the main assemblages simplyfive. Each big or medium-sized oilfield basically consists of one assemblage which in turn has one main oil or gas pool. With the variation of structural condition and sedimentary facies. the above mentioned flve type assemblages of oil and gas pools distribute basically around the oil source area in annular zones. The central part of the depression is favourable to the formation of the oiland gas assemblage of central uplift zone in which arcogene sistensile anticlineand faulted anticline predominates

and the assemblage of inside depression in which the lithologic pool of turbidite predominates. The slope area of the depression is favourable for the formation of slope zone assemblage in which oil and gas pools of overlap

buried-hill on slope and reverse-dipping fault block predominate. The margin of the depression

especially the steep side

is favourable to form the assemblage of the marginal anticline zone and marginal depression zone. The uplift area from the lower part to the top is favourable to form the assemblages of various buried hill-draped structural zones.