Liquid-liquid equilibrium (LLE) data including solubility curves and tie-line compositions were measured for mixtures of water (1) + formic acid (2) + dimethyl succinate or dimethyl glutarate or dimethyl adipate (3) at T = 298.2 K and atmospheric pressure, p = (101.3 +/- 0.7) kPa. The relative mutual solubility of the formic acid is higher in the aqueous phase than in the dibasic ester phases. The reliability of the experimental tie-line data was confirmed by using the Othmer-Tobias correlation. The LLE data of the ternary systems were predicted by UNIFAC and modified UNIFAC methods. Distribution coefficients and separation factors were evaluated for the immiscibility region.