Liquid-liquid equilibrium data were measured and correlated for the ternary systems acetonitrile + water + heptanoic acid and acetonitrile + water + nonanol at 323.15 K and 1 atm. The liquid-liquid equilibrium data were measured using the direct analytical method in a double-walled glass cell. The binodal curve was correlated using a modified Hlavaty equation, a beta function, and a log gamma equation. The experimental tie lines were correlated using the NRTL and UNIQUAC activity coefficient models. Fitting of both activity coefficient models was undertaken by nonlinear least-squares regression of the data. The tie-line data were used to derive the selectivity values for solvent separation efficiency.