(Liquid + liquid) equilibrium (LLE) data of the solubility (binodal) curves and tie-line end compositions were examined for {water (1) + propionic acid (2) + diethyl succinate or diethyl glutarate or diethyl adipate (3)} at T = 298.15 K and 101.3 +/- 0.7 kPa. The relative mutual solubility of the propionic acid is higher in the dibasic esters layers than in the aqueous layers. The reliability of the experimental tie-line data was confirmed by using the Othmer-Tobias correlation. The LLE data of the ternary systems was predicted by UNIFAC method. Distribution coefficients and separation factors were evaluated for the immiscibility region. (c) 2007 Elsevier Ltd. All rights reserved.