Distributions and geochemical significances of 18a (H)-neohopanes and of 17a (H)- diahopanes in oils from west Xialiaohe depression of the Bohai Bay Basin have been studied.Relative abundance of 18a (H)-neohopanes and of 17a (H)-diahopanes can be effectively used as maturity parameters,in a range of medium-high mature stage,based on consideration on sedimentary-organic facies of source rocks.With a dual geochemical significance of maturity and sedimentary-organic facies,neohopane and diahopane parameters can be well used in oil-source correlation and in petroleum population division.Formation,primary concentration and preservation of precursors of rearranged hopanes are closely related to depositional conditions such as Eh-pH and clays content.A series of probable diahopanes (series D) was detected in the oils,which exhibits a similar distribution pattern and geochemical behavior as that of 17a (H)-diahopanes (series B).