Solution properties of perfluorononanoic acid and of its alkali metal salts, as well as of lithium, sodium and potassium perfluorooctanoates have been studied by surface tension, volumetric, colligative, emf and electrical conductance experiments and were supported by studies on phase equilibria, performed in close proximity to the CMC.Thermodynamics of micelle formation has been analysed both in terms of a charged-phase model and according to an isodesmic multiple equilibrium approach so as to account for counterion effect on micellization and for the cooperativity of micellar association, respectively.