The dynamic interfacial tension in surfactant/alkali/acidic oil systems was investigated in a mode of three arylalkyl surfactant flooding. The results indicate that there exists an optimum range of alkali concentrations when the minimum interfacial tension value is below 10(-2) mN/m (the ultra-low interfacial tension value) at certain surfactant concentrations. The minimum interfacial tension presents a similar parabolic relationship with alkali concentrations and also a similar hyperbolic relationship with surfactant concentrations as well. Thus, a convexity can be built by the results of three variables, i.e., the minimum interfacial tension, surfactant concentration, and alkali concentration. The capability of synthesized arylalkyl surfactants in reducing the interfacial tension can be expressed by the values of the volumes formed by the three variables. The higher value indicates the stronger capability of the surfactant in reducing the interfacial tension. This method for the capability of surfactant being quantified would offer a new way to choose the surfactants in enhanced oil recovery.