Solubilities of pyridine-2-azo- p -dimethylaniline ( pada ) were determined at 25ºC in four mixed fluorocarbon/hydrocarbon short-chained surfactant systems: ( i ) sodium decyl sulfate/sodium perfluoroheptanoate; (ii) sodium octanesulfonate /sodium perfluorooctanoate ; (iii) sodium octanesulfonate /sodium perfluoroheptanoate ; (iv) sodium nonanesulfonate /sodium perfluoroheptanoate. Systems ( i ), (iii) and (iv) showed micellar miscibility (one mixed micelle) and synergistic solubilization effects. System (ii) had two critical micelle concentrations pointing to two micellar forms in solution, and no synergism could be detected. From these four examples, it is deduced that single mixed micelles are formed when the critical micelle concentrations of the pure surfactants are within a factor of 3 of each other.