Gunan Say is located in Jiyang Depression

Bohai Bay Basin. Based on the characteristics of its source rocks

pool-forming evolution and distribution

the sag can be divided into two pool-forming systems

i. e. petroleum accumulation system I and the system Ⅱ. The main source rock of the system I is the third member of Shahejie Formation

hydrocarbon generation threshold was in the end of Oligocene

and now it is highly matured. The reservoir rocks of the system I are distributed from Mesozoic basement to Neogene clastic rocks. The source rock of the system Ⅱ is the first member of Shahejie Formation

its hydrocarbon generation threshold was in the end of Miocene

and now is lowly matured;the reservoir rocks are mainly distributed in the first and second members of Shahejie Formation and Dongying Formation. Although the source provinces of the two systems are generally superposed

the distribution and propenies of hydrocarbon are different. System I stretches bo the intrasag to surrounding uplifts

while system Ⅱ streches to the intrasag only. Besides their migration and accumulation ways are different.