Abstract: By comparisons of the petroleum gevlogic conditions between Dongpu sag and Dongying sag in Bohai Bay basin, the reasons for the differences in hydrocarbon resources and 3D spatial distribution of these two sags are presented. The study shows that Dongpu sag is not as superior as Dongying sag in shallow reservoir?forming condition. It has the possibility of small?scale hydrocarbon accumulation or reservoir?forming, but the control factors are extremely complex. The main reasons are as follows: the abundance and quality of source rocks in Dongpu sag are poor and difficult for preservation, with a large proportion of natural gas in its generated hydrocarbons; a great quantity of hydrocarbon generation and formed traps appear in late Dongying formation, hence there exist a large quantity of oil and gas dispersion and loss; because of little hydrocarbon generation and weak fault activity in the Neogene, the oil and gas migration toward the shallow strata is short of power and channel, and unfavorable for shallow reservoir?forming in this sag