Jiyang (济阳) sag is an oil rich basin, consisting of Huimin (惠民), Dongying (东营), Zhanhua (沾化), and Chezhen (车镇) depressions. The clastic rock of Paleogene has undergone early and middle diagenetic stages and now the main clastic reservoir is in the middle diagenetic stage. Primary and secondary pores are developed in Paleogene sandstone, the latter is generated from the dissolution of feldspar and calcite cement in rocks owing to the organic acid from the maturated source rock, but the materials dissolved are different in different depressions. The reservoir secondary pores of Dongying depression are generated from the dissolution of calcite cement, the ones of Zhanhua and Huimin depressions from the dissolution of feldspar, the secondary pores of Chezhen depression from the dissolution of feldspar in upper section, and the dissolution of calcite cement in the lower section of Paleogene, respectively. The secondary pores are developed in two depths and the depth goes down from west to east, from south to north in Jiyang sag. The major controlling factors for secondary pore development are maturity and location of source rock. Lastly, the favorable reservoirs are evaluated according to reservoir buried depth, sedimentation, and diagenesis. The reservoir with high quality is located in the northern and central parts in Dongying depression; there are some good reservoirs in Gudao (孤岛), Gudong (孤东), and Gunan (孤南) areas in Zhanhua depression, and the favorable res- ervoirs are located in the north steep slope and the south gentle slope of Chezhen depression and central uplift, south gentle slope of Huimin depression. Jiyang sag is an oil rich basin, consisting of Huimin, Dongying, Zhanhua, and Chezhen depressions. The clastic rock of Paleogene has undergone early and middle diagenetic stages and now the main clastic reservoir is in the middle diagenetic stage. Primary and secondary pores are developed in Paleogene sandstone, the latter is generated from the dissolution of feldspar and calcite cement in rocks due to the organic acid from the maturated source rock, but the materials dissolved are different in different depressions. the reservoir secondary pores of Dongying depression are generated from the dissolution of calcite cement, the ones of Zhanhua and Huimin depressions from the dissolution of feldspar, the secondary pores of Chezhen depression from the dissolution of feldspar in upper section, and the dissolution of calcite cement in the lower section of Paleogene, respectively. The secondary pores are developed in two depths and the depth goes Down from west to east, from south to north in Jiyang sag. The major controlling factors for secondary pore development are maturity and location of source rock. Lastly, the favorable reservoirs are evaluated according to reservoir buried depth, sedimentation, and diagenesis. The reservoir with high quality is located in the northern and central parts in Dongying depression; there are some good reservoirs in Gudao, Gudong, and Gunan areas in Zhanhua depression, and the favorable res-ervoirs are located in the north steep slope and the south gentle slope of Chezhen depression and central uplift, south gentle slope of Huimin depression.