In the present study, four surface-active ionic liquids (SAILs) having different head groups (phosphonium, pyridinium, pyrrolidinium, and imidazolium) but the same hydrophobic tail length and same anion attached have been screened for their surface activity and capability in reducing interfacial tension (IFT) between crude oil and water. Effects of increasing NaCl concentration and alkali addition on the IFT between crude oil and SAIL solution have been studied. It is known that alkalis react with naphthenic acid present in the crude oil and form an in situ surfactant. This in situ surfactant when injected with some SAIL further lowers the IFT between crude oil and water. Phase behavior studies have been performed to determine the formation of a WINSOR III phase in ternary systems containing NaOH + SAIL/brine/crude oil or model. To compare the efficiency of NaOH + SAIL combinations over individual SAILs for application in enhanced oil recovery (EOR) processes, five core flooding experiments have been performed. The NaOH + pyrrolidinium/imidazolium-based SAIL lowered IFT to ultralow values at optimal salinity as high as 15 wt % NaCl and thus recovered more oil than the individual SAILs. It can be concluded that some NaOH + SAIL combinations can be used in surfactant-assisted EOR processes in carbonate reservoirs having a high salinity (similar to 15 wt % NaCl) environment.