Ternary liquidliquid equilibrium (LLE) data were measured and correlated for the water + acetonitrile + (butan-1-ol or 2-methylpropan-1-ol) systems at (303.2, 323.2, and 343.2) K and 1 atm. A double-walled glass cell with the direct analytical method was used to measure the liquidliquid equilibrium data. The phase equilibrium samples were analyzed and quantified using gas chromatography. The nonrandom two-liquid activity coefficient model was used to fit the experimental tie-lines using nonlinear least-squares regression of the data. Relative selectivity values for solvent separation efficiency were calculated from the tie-line data. The plait point for each temperature was estimated with the graphical Coolidge method.