The tie-line and solubility data, i.e. formic acid (FA) + n-butanol + water + NaCl, were resolved at T=298.15K and under ambient pressure. The Othmer-Tobias equation was applied in this study. The experimental data were correlated and all linear correlation coefficients were found to be approximately equal to 1. Both the Universal Quasi-chemical Theory (UNIQUAC) and Nonrandom Two Liquid Theory (NRTL) and NRTL models were employed in order to compare the experimental liquid-liquid equilibrium (LLE) and tie-line data. Consequently, the calculated and experimental data proved to be a good fit. Results show that adding salt to the system proved beneficial by increasing the separation of FA from water.