The liquid-liquid equilibria in ternary systems 2-methylbutane + 2-methyl-2-propanol + water and pentane + 2-methyl-2-propanol + water were experimentally determined at 293.15 K by direct analytical methods and a titration method. The ternary data along with other thermodynamic data of binary subsystems previously published were utilized for a thermodynamic description of the systems. The original UNIQUAC model was combined with a ternary term. Binary parameters of the model were considered to be temperature dependent, and they were calculated employing the maximum likelihood method. Ternary parameters were evaluated using a nonderivative numerical procedure.