Free energy of nanoparticles can increase the surface activity at the solid/oil/liquid contact line and remove oil through the disjoining pressure gradient mechanism. Surfactants can also remove oil mainly by reducing interfacial tension, although raising economic concerns as a result of their adsorption on the rock surface. Introduction of nanoparticles to surfactant solutions seemed to be more prominent in improving the wettability than reducing the interfacial tension, which could offer an opportunity to develop cost-effective chemical flooding agents to enhance oil recovery in carbonate reservoirs. However, characterization of wettability alteration using contact angles typically fails in providing consistent results. In this study, the dual-drop-dual-crystal technique was employed to measure precise and reproducible dynamic contact angles and was supported by relative permeability curves generated by coreflood experiments to evaluate the wettability alteration performance of silica nanoparticles combined with both effective and ineffective anionic surfactants at both ambient and high-pressure, high-temperature conditions. Adding nanoparticles to surfactants was seen to change the wettability of the carbonate rocks from strongly oil-wet to weakly oil-wet and intermediate-wet conditions (e.g., change in the advancing contact angle from 167 degrees to 98 degrees), which improved the oil recovery (up to 93% of the original oil in place) and reduced the residual oil saturation, without having to significantly reduce the interfacial tension (only 1 or 2 orders of magnitude). Reduction of the surfactant concentration in the combination did not significantly hinder the wettability alteration performance, showing the ability of nanoparticles to compensate for surfactants. Therefore, the combination of nanoparticles and low-cost dilute surfactants can be tuned to provide economically appealing chemical flooding agents to enhance oil recovery.