<![CDATA[Surfactant flooding is an Enhanced Oil Recovery (EOR) technique aimed at improving oil displacement efficiency by reducing the interfacial tension (IFT) between oil and water. This study investigates the performance of palm oil–based Methyl Ester Sulfonate (MES) surfactant combined with 96% ethanol as a co-surfactant for EOR applications. The surfactant formulations were prepared at MES concentrations ranging from 0.5% to 2.0% and evaluated through density, viscosity, aqueous stability, phase behavior, interfacial tension, and coreflooding experiments. The aqueous stability test showed that all formulations remained clear without precipitation, indicating good thermal stability. Viscosity measurements showed that solution viscosity increased with higher surfactant concentrations but consistently declined as the temperature rose from 30 °C to 60 °C. Phase behavior analysis demonstrated that ethanol enabled the formation of emulsions at all concentrations, with middle-phase microemulsions observed at MES concentrations of 1.25% and 1.5%. The largest middle-phase emulsion volume of 3.00% was obtained at 1.25% MES, indicating the optimal formulation. Interfacial tension measurements showed a reduction to 0.521 mN/m, confirming the effectiveness of the co-surfactant in lowering IFT. Coreflooding results indicated that surfactant injection yielded an incremental oil recovery factor of 29.24% over conventional waterflooding, achieving a total cumulative recovery factor of 45.90%.]]>
