<p>Conventional macroscopic approaches to reserve estimation and productivity forecasting are inadequate for assessing shale oil systems characterized by heterogeneous wall-surface wettability and nanoscale confinement effects. As such, a deeper understanding of the microscale mechanisms governing shale oil occurrence, along with robust quantitative characterization methods, is essential. This study focuses on clay-laminated shale oil from the Cretaceous Qingshankou Formation in the Songliao Basin, employing a combination of swelling-extraction experiments, SEM-AFM pore structure analysis, and advanced molecular dynamics (MD) simulations to explore how multi-component shale oil is distributed within slit-like pores of clay minerals and various kerogen types. The results demonstrate that the kerogen-based model provides a more precise representation than the graphene model in capturing the impacts of organic matter composition, oil component polarity, and varying pressure-temperature conditions on adsorption behavior. Based on a spherical-pore model and fractal theory, we establish a specific surface area evaluation model that couples porosity, pore size distribution, and surface roughness. By integrating MD-derived swelling parameters with their evolution across thermal maturity stages, a ternary quantitative occurrence model was developed, encompassing swelling-bound, adsorbed, and free oil states. The model delineates distinct maturity-dependent transitions: kerogen-swelling oil predominates at low maturity; free oil accumulates rapidly during the mature stage; and compaction at high maturity leads to a moderate decline in free oil content. Clay-laminated Qingshankou shale oil, characterized by high clay mineral content and abundant organic matter, serves as a representative case. Based on above new methodology, the free oil resource in Member 1 of the Qingshankou Formation is estimated at 0.94×10⁹ t. In the northern upper sub-member (Q8–Q9 reservoirs) of the Gulong Sag, free oil is predominantly enriched in inorganic pores (up to 9.0 mg/g), whereas in the lower sub-member (Q1–Q4 reservoirs), it is mainly hosted within organic pores (up to 6.0 mg/g). The upper sub-member of the Qijia Sag shows development potential (7.0–10.7 mg/g inorganic-pore free oil). In contrast, the Sanzhao Sag and Changyuan Anticline currently lack conditions for large-scale economic development because free-oil contents are &lt;4.0 mg/g. The occurrence-state framework and quantitative characterization method proposed here provide a multiscale quantitative tool for sweet-spot selection and development scheme design in shale oil plays.</p>