A total of 6 oil samples were systematically selected from six Asmari Reservoir wells in the Cheshmeh-Khush Oilfield for geochemical evaluation of the hydrocarbon system, based on reservoir geochemistry and oil fingerprints. An investigation of the distribution patterns of normal alkanes and tricyclic and tetracyclic terpanes along with characteristic biomarkers of the depositional environment and sedimentary facies, indicated that the source rock of the studied hydrocarbons was deposited in a reducing aquatic environment with a low input of terrigenous material and predominantly carbonate lithology derived from organic algal matter. The studied oil samples exhibited moderate maturity, as was further confirmed by the parameters extracted from the light hydrocarbons. Statistical clustering based on different biomarker parameters indicated the presence of two oil families. Additionally, the application of branched and cyclic compounds in the light hydrocarbons (C5–C11) to evaluate lateral continuity of the Asmari reservoir further supported the presence of the two oil families. Other evidence proved the presence of a NE–SW trending fault separating wells X5 and X6 from the other wells in the field. In other wells across the field, good lateral reservoir continuity was observed, despite the presence of faults on the northern and southern plunges of the structure.