Three pure mid-position phenyltetradecane sodium sulfonate isomers were synthesized. The capabilities for lowering the interfacial tension of three isomers were different, the sequence being 7-phenyltetradecane sodium sulfonate > 5-phenyltetradecane sodium sulfonate > 3-phenyltetradecane sodium sulfonate. The effects of minimum dynamic interfacial tension in alkane/aqueous system as a function of alkalinity of three isomers were also different. The discrepancy was elucidated from the view of the structures against an imaginary interfacial molecular arrangement model. Moreover, the interfacial tension behavior against crude oil proved that the capability for lowering interfacial tension was governed by the essential difference in structure and would not be altered with the oil phase.