Current concerns about adverse impacts to the environment and human health have encouraged the research and development of renewable fuels, such as biodiesel. The transesterification reaction is a three-stage reaction, which produces two intermediate products (diacylglycerols and monoacylglycerols). Accurate and proper knowledge of the phase equilibrium behaviour during the transesterification process is crucial for a better understanding of the reaction pathway, for the optimisation of reactors and the separation of the products. Thus, in order to thoroughly understand the entire transesterification system for biodiesel production, which consists of six different kinds of components, this study reports experimental results and the thermodynamic modelling of the (liquid + liquid) equilibrium (LLE) of two systems composed by {vegetable oils (sunflower or high oleic sunflower oils) + monoacylglycerols + diacylglycerols (+ ethyl esters + fatty acids) + ethanol} at T = (303.15 and 318.15) K, at atmospheric pressure. The LLE experimental values were used to estimate NRTL parameters and to evaluate the UNIFAC model, using its original version with two different set of parameters. Results showed that, due to differences in the number of polar groups, mono- and diacylglycerols behave in opposite ways regarding phase distribution. Experimental data were well correlated using NRTL, in which the maximum deviation value was 0.434%. As for UNIFAC, the model predicted the experimental data with deviations varying within the range of (1.80 to 9.24)%. (C) 2015 Elsevier Ltd. All rights reserved.