The western Liaohe depression began its developing at Oligocene and kept on sinking ever since.Now

the thickness of sediments with abundant organic matters reaches 5

000—6

000m.Because of the later Tertiary fracturings and foldings resulting from the progressive warping and epigenetic tectonic movements

sequences of source rocks and varieties of traps favourable to oil and gas generation and accumulation were formed.Four catigories of oil and gas pools are found

which are subdivided into nine types of different traps

such as:1).tectonic pools

including a).anticline;b).faulting blocks;and c).faulted structural noses;2).stratigraphycal pools

including d).overlaps;and e).uncomformities;3).basement pools

including f).latent ridges;and g).uncomformities of base-ment;and 4).lithological pools

including h).lenticular sandstones;and i).pinched layers.All these pools are regularly distributed in different parts

superimposing each other.They can be summarized as two series of oil and gas pools:1).anticlinal series and 2).slope series.They can be used as models for arranging exploration and appointing places favourable to oil and gas searching.The depression appears in shape of dustpan.Therefore

the oil and gas traps were formed in direction from margin to centre;whereas maturation of oil and gas began from central parts towards margin.This kind of relationship between tectonic and oil generation processes implies certain regularities of special distribution of oil and gas pools and can lead to discovering of possible pools in some places else.