Enhancing oil recovery (EOR) is critical for maximizing hydrocarbon extraction from reservoirs, yet conventional methods often face limitations in efficiency. In recent years, nanoparticles have been increasingly applied to enhance oil recovery techniques due to their unique properties. This study proposes surface-modified zinc oxide nanocomposites (ZLO) at an optimized concentration as a novel EOR agent. The performance of ZLO was systematically evaluated and compared with conventional zinc oxide nanoparticles (ZnO) under identical experimental configurations replicating reservoir conditions. This investigation employed a comprehensive suite of characterization techniques, including wettability alteration analysis, interfacial tension measurements, and zeta potential determination, to evaluate the nanofluid’s properties. The main novelties of this study are: (1) its identification of the optimal concentration of ZLO and ZnO; and (2) performing recovery factor determination through spontaneous imbibition at real reservoir conditions. Following the examination of ZnO and ZLO nanocomposite crystalline structures, the ZnO and ZLO nanofluids were used at concentrations ranging between 5 and 30 ppm to determine the optimum concentration of each material. Comprehensive analysis of colloidal stability (via zeta potential) and wettability modification (via contact angle) revealed that 10 ppm represented the optimum concentration for both ZnO and ZLO nanoparticles in EOR applications. At 10 ppm, the contact angle and zeta potential reached (59.28°, -31.38 mV) and (41.04°, -42.78 mV) for ZnO and ZLO, respectively. After 15 days of imbibition operations, the oil recovery factors for the base, ZnO, and ZLO solutions were 24.95%, 35.74%, and 62.41%, respectively
