Micellization of binary systems of a cationic gemini surfactant butanediy1-1,4-bis(dimethylcetylammoniurn bromide) (16-4-16) and cationic/nonionic hydrotropes (aniline-hydrochloride, 2-methylanilinehydrochloride, 4-methylanilinehydrochloride, hydroxybenzene, 1,3-benzenediol, benzene-1,2,3-triol) have been studied using a conductometric technique. The critical micelle concentrations (cmc) for different mixing mole fractions at different temperatures have been calculated. To explain and compare the results, theoretical models of Clint, Rubingh and Motomura have been used to obtain the ideal cmc, mixed micelle composition, interaction parameters (beta(m)), free energies of micellization, and activity coefficients. The mixtures show nonideal behavior and the interactions between the surfactants and the hydrotropes are synergistic in nature which is confirmed by high negative beta(m) values and low values of the activity coefficients. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values. (C) 2011 Elsevier Inc. All rights reserved.