In this study, organic-rich inter-salt shale facies (ISSF) of the Eocene Bahadur Khel Salt from outcrop section in the Kohat Basin was studied. Multi-scale organic geochemical and petrological analyses in combination with elemental analysis and mineral composition were carried out and used to assess the organic matter (OM) input, main paleoenvironment, factors and then interpreted the organic carbon enrichment influence. This research also aims to understand the unconventional shale oil reservoir potential of the ISSF. The ISSF exhibit high total organic carbon (TOC) and sulfur (S) concentrations, with high S/TOC ratio exceeding 1 in most samples, suggesting deposition under highly reducing marine environmental conditions. This interpretation is further inferred by the biomarkers and trace elements of redox sensitivity, with a narrow Pr (pristane)/Ph (phytane) ratio < 1, and high C-35/C-34 homohopane ratio in combination with high V/Ni ratio of greater than 3. The occurrence of pyrite within the ISSF is also confirmed a poorly oxygenated environment, which is likely formed through the sulphidation of iron under low-oxygen conditions via microbial sulphate reduction in pore waters. Moreover, high abundant gammacerane biomarker together with paleoclimatic indicators also suggests the ISSF was deposited in hypersaline environment under semi-arid climate, leading to low-moderate bioproductivity. Consequently, the preservation mode under the intensity of reducing conditions is the primary controlling factor for OM accumulation in the ISSF. Molecular biomarker evidence also indicates that the OM within the ISSF is primarily derived from marine organisms of bacteria and algae, with minimal input from terrigenous plant. This evidence is supported by elevated tricyclic terpane ratios and a higher proportion of C-27 and C-29 regular steranes relevance to C-28 regular sterane. This high abundance of aquatic organisms in ISSF of the Bahadur Khel Salt suggests indigenous OM deposition as hydrogen-rich kerogen of Types II and II/III. This finding is consistent with the current hydrogen index (HI) values between 204 and 548 mg HC/g TOC, and suggests oil and gas source rock, with mainly oil generation potential. However, the ISSF is oil-saturated rock and reached commercial amounts for a possibility of oil production, as supported by the higher values of oil saturation index (OSI) of > 100 mg HC/g rock for most of the studied samples. This high oil saturation, alongside higher brittleness minerals (i.e., quartz and carbonate) than ductile clay mineral leads to create non-fabric fracture pores, which they may have increased by elevated pressure during their deep burial. Thus, depending on the other prerequisites of an unconventional reservoir, further exploration of ISSF of the Bahadur Khel Salt is recommended in its subsurface stratigraphic equivalent within the Kohat Basin.