Recent Chinese shale oil (or gas) exploration efforts have focused on the Shahejie Formation of Bohai Basin. However, this work has been handicapped by a lack of state-of-the-art investigations of the targeted shale. Specifically, there is a need for an improved understanding of the role that paleoenvironmental aspects of the basin played in the organic enrichment of these deposits. The present study provides the insights into the paleoenvironmental and depositional history of various of shales of the Es₁ Member of Paleogene Shahejie Formation, Qikou Sag, Bohai Basin, and addresses the controlling factors of organic matter (OM) accumulation and preservation in these deposits based on petrographic characteristics, organic geochemistry, and major and trace elements data. Our results suggest that the organic-enriched Es₁ oil shale is a desirable exploration target, especially felsic and mixed shale. The felsic shale, mixed shale, dolostone and carbonate shale accumulated under relatively humid climatic conditions but in saline lacustrine environment. Climate, salinity, and redox conditions appear to have varied at least three times during the depositional history of the studied interval. Paleoenvironmental conditions favored stable productivity levels and only a modest supply of clastic detritus sediment resulting in a diminished rate of deposition. Felsic and mixed shale deposits that have the greatest source potential accumulated under more humid atmospheric and oxygen-depleted environmental conditions than dolostone and carbonate shale. The present study suggests infers that organic carbon content of the Es₁ oil shale was controlled principally by salinity and secondarily by primary productivity and redox conditions.