Abstract: The Jiergalangtu Sag in the Erlian Basin is rich in shale oil and gas resources with significant exploration potential. However, the oil content, pore structure characteristics, and controlling mechanisms of its Cretaceous shale oil reservoirs remain unclear. By employing a combination of total organic carbon (TOC), conventional Rock-eval pyrolysis, multistage Rock-eval pyrolysis, X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, high-pressure mercury injection, and one-dimensional/two-dimensional nuclear magnetic resonance (NMR), this study systematically reveals the oil content and full-scale pore-throat distribution characteristics of shale oil reservoirs, while exploring the coupling relationships between oil content, mineral composition, and pore structure. The results reveal that the shale in the lower first member of Tengger Formation (K₁bt₁) demonstrates higher organic matter abundance and superior storage properties compared to the fourth member of Aershan Formation (K₁ba₄). It features more developed large pores and throats, which enhance shale oil storage and flow. Conversely, the shale in the K₁ba₄ has lower organic matter abundance, with micropores and throats dominating, resulting in poorer storage and flow. The development of pores and throats is primarily influenced by TOC and clay mineral content. High TOC and low clay mineral content favor the formation of macropores and throats in the lower K₁bt₁, enhancing its storage and flow properties. However, higher TOC may inhibit the development of macropores and throats in the K₁ba₄. Shale oil content is jointly determined by TOC, maturity, and pore structure, with TOC being the most critical factor, particularly for the K₁ba₄. The research results provide an important basis for evaluating “sweet spots” in shale oil reservoirs within the Jiergalangtu Sag.