The commercial production of shale oil in onshore Bohai Bay Basin has become a reality, but the potential of offshore shale oil is still unclear. The Bohai Sea, the leading crude oil-producing area in China in 2022, has great potential of shale oil resources, but the shale properties have not been comprehensively studied. The southern Bohai Sea, including the Huanghekou and southwestern Bozhong Sags, was selected. The study was performed on three layers: the third member of Shahejie Formation, first and second members of Shahejie Formation (as a whole), and the third member of Dongying Formation. Twenty-one shale core samples from nine wells, for the first time, were analyzed for sedimentary structure, lithology, pore space, composition of the thermally hydrocarbons and oil content. The content of minerals, pore sizes, and composition of the thermally hydrocarbons were compared with those of shales from other regions of China. The potentially producible oil generated in the organic-rich laminae was found to be accumulated in the silt-grained laminae through micromigration. Mixed and siliceous shale were the main lithofacies. Mineral overgrowths and solid bitumen reduce the volume of former intergranular pores. Honeycomb-like OM pores in samples with higher maturity (Ro > 1.1%) substantially increased pore connectivity from FIB-SEM image datasets. The retained oil was mainly distributed in pores with widths larger than 4 nm. The composition of the thermally hydrocarbons in samples stored at ambient conditions was governed by the maturity and concentration of the OM. Light hydrocarbons, even gaseous hydrocarbons are still retained in the shale with lower maturity and higher TOC for strong sorption of OM. The oil content is 0.50–23.41 mg/g after Rock-Eval S1 correction, with an average of 6.27 mg/g. While average oil content is 1.38 mg/g without correction. Finally, the optimal production intervals for Well B4 and Well B8 were determined. This study provides data and suggestions for the exploration of shale oil resources in the southern Bohai Sea.