Osmotic coefficients phi of aqueous solutions of 1-n-decanepyridinium chloride, 1-n-dodecanepyridinium chloride, and 1-n-hexadecanepyridinium chloride are estimated at T = 328.15 K from vapor pressure osmometric measurements. Molar integral enthalpies of dilution Delta(dil)H(m) have been measured for aqueous solutions of these surfactants, and also for aqueous solutions of 1-n-tetradecanepyridinium chloride, at T = (283.15, 298.15, 313.15, 328.15, and 343.15) K. Measurements were made, where possible, at molalities from well below to well above the critical micelle molality m(cmc). Values of phi and Delta(dil)H(m) for each surfactant were treated using a mass-action model that includes ion-interaction terms for the activity coefficients of both micellar and monomeric ionic species in solution. The ion-ion interaction parameters were estimated from values of phi reported in this investigation and from values reported in the literature. The temperature coefficients of these parameters were estimated from values of Delta(dil)H(m) Treatment of Delta(dil)H(m) With the model also leads to values of Delta(r)H(m) degrees for the reaction of monomeric surfactant and Cl-(aq) to form micelles, and to the corresponding values valid at finite molalities, including m(cmc). Fitting all values of Delta(dil)H(m) simultaneously for a surfactant yields numerical values of a small number of parameters for equations that represent its behavior in terms of an equilibrium constant, an activity coefficient equation, and their temperature derivatives. Systematic trends in measured properties and derived parameters as functions of molality, temperature, and surfactant structure are discussed briefly.