Ternary liquid-liquid equilibrium (LIP) data of 2-methyl-2-propanol + 1-pentanol + water under atmospheric pressure were investigated at T = (303.15, 328.15, and 353.15) K, respectively, in this paper. The consistency of the tie-line data obtained by the experiment was determined using the Othmer-Tobias and Bachman equations Moreover, the measured data were correlated with the nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) activity coefficient models. The excellent ability of both models for calculating the LLE of the studied system was confirmed by comparing the correlated values and the experimental values.