Enhanced oil recovery (EOR) is considered a crucial strategy for optimizing the extraction of hydrocarbons from established reservoirs, so far traditional techniques frequently encounter difficulties in challenging salinity, temperature, and reservoir heterogeneity conditions. Surfactants are essential for boosting oil mobilization, changing wettability, and lowering interfacial tension. The synergistic utilization of mixed surfactant systems, which perform better physicochemical than the individual surfactants, is highlighted by recent studies. This chapter provides a comprehensive overview of surfactant systems, including their various forms, essential traits, and methods of operation in porous media. In addition to that, thermodynamic models and molecular interactions are utilized to study the fundamentals of synergism, and then experimental and theoretical methods are employed to describe the synergistic effects of the mixed surfactant systems. The potential of surfactant combinations such as anionic-cationic, anionic-nonionic, gemini-conventional, etc., systems to improve oil recovery across sandstone and carbonate reservoirs is demonstrated by different case studies and their practical applications. Besides, important issues are also covered, such as formulation stability, surfactant adsorption, and environmental concerns. Finally, future prospects are drawn with an emphasis on integrating nanotechnology, polymers, green surfactants, and computational modeling to develop economical and sustainable surfactant formulations for the next generation of EOR systems.