Mudstone reservoirs discovered so far in the Jiyang Depression is mainly distributed around the faulting and nose-like structures in the Dongying Sag,Zhanhua Sag and so on. According to the storage space, three types could be classified:fissure type,pore type and pore-fissure compound type oil-gas accumulations. The fissure type one was predominates and mainly developed in brittle and calcium-rich mudstones and shales. The pore type one occurred mainly in under-compacted and sandy strip-bearing mudstones, and the pore-fissure compound type one developed in the rocks of calcium mudstone-shale interbeds with partings of lamella sandy strips.The mudstone reservoirs were characterized mainly with self-generation and self-storage,which needed some special lithological conditions such as abundant calcium or under-compaction, etc.,and distributed generally near the active fault zones,nose-like structures and fault-uplift structures.Laterally,the fissure type oil-gas accumulations distributed mostly in the thick matured hydrocarbon source rocks with rich calcium and high electrical resistivity,especially in the thin interbeds with well-developed shale. The pore type oil-gas accumulation distributed only in the under-compacted region with rich sandy strips on the background of faulting or fault-uplift structures.Vertically,the mudstone reservoirs distributed mostly in the layers of well depth below 2 200 m, which were the strata of the upper sub-member of Member 4, Shahejie Formation,the lower sub-member of Member 3, Shahejie Formation and the the lower sub-member of Member 1, Shahejie Formation.