Two zwitterionic surface-active ionic liquids (SAILs), 3-(1-hexadecyl-3-imidazolio) propanesulfonate (C16IPS) and 3-(1-hexadecyl-3-imidazolio) propanesulfonate beta-naphthalenesulfonate (C16IPS-Nsa), were evaluated for their potential application in chemical enhanced oil recovery. It was found that the zwitterionic SAILs had a higher interfacial activity than the traditional SAILs. Interestingly, the C16IPS-Nsa molecule with the large hydrophobic group beta-naphthalenesulfonate had a greater ability for reducing the interfacial tension (IFT) of water/crude oil. Moreover, the systematic investigations of the dynamic IFT and the salt and temperature effects further confirmed the proposed mechanism of two zwitterionic SAIL effects on the IFT. The C16IPS-Nsa system exhibited a satisfactory displacement performance (15.3% of initial oil in place), which may be attributed to the transient minimum value (similar to 1 x 10(-3) mN/m) in its dynamic IFT curve.