Reverse structures in Songliao basin are mainly wide and gentle folds and placanticline with small deformation.The reverse structures have been formed in three differant stages:at the end of deposition of Nenjiang Formation in Late Cretaceous

at the end of deposition of Mingshui Formation and Late Cenozoic.The strongest reverse structural action that occurred at the end of deposition of Nenjiang Formation would have the largest effect on hydrocarbon accumulation in Songliao basin

including (a) reverse structures provide traps for hydrocarbon accumulation; (b) reverse structural actions promote remigration of hydrocarbons; and (c) reverse structures result in many fractures and thus improve the poroperm characteristics of reservoir rocks.