Liangjialou oilfield in Dongying sag,Bohai Bay basin,was previously thought to be an"indigenously generating and accumulating"oil reservoir,i.e.hydrocarbons generated in the mudstones in the middle 3rd member of Shahejie Formation have migrated upward into the adjacent turbidite glutinite.This view,however,is not supported by the latest achievements in hydrocarbon source rock studies in Dongying sag.Oil-to-source correlation,hydrochemical characteristics of oil reservoir and reservoir pressure show that oil reservoirs in southern Liangjialou oilfield,mostly characterized by superpressure and chloride-calcium type water,have been sourced by the upper 4th member of Shahejie Formation,i.e.hydrocarbons have firstly migrated laterally along the pathways in the rocks,and then migrated vertically upward through faults and become oil reservoirs either of "both generated and accumulated indigenously"or"generated below and accumulated above";while those in middle and northern Liangjialou oilfield,characterized by normal pressure and sodium bicarbonate water,hydrocarbons have been generated in the lower 3rd member of Shahejie Formation, and then directly migrated vertically through faults in the source rock,so the oil reservoirs are of the type of "generated below and accumulated above". The knowledge enlightened us to reevaluate the source rocks in the middle 3rd member of Shahejie Formation and restudy the pool-forming patterns in the similar pools around the center of the sag.