Biodiesel production consists of several processes, the reaction stage being the most important. However, after reaction, the biodiesel product undergoes separation involving an aqueous phase, hence, the need for accurate information on liquid-liquid equilibrium (LLE) parameters of mixtures formed by biodiesel, alcohol, glycerol, and the aqueous phase. We here performed experiments on ternary and pseudoquaternary systems of sunflower biodiesel to gather data to estimate binary interaction parameters for LLE using the UNIQUAC model. Our results showed that temperature had essentially no effect on ternary systems, with a small reduction of the immiscibility region at 318.15 K. As for the pseudoquaternary systems, we observed that by increasing the amount of the aqueous phase from 50 to 75%, the region of phase separation increased, and the solubility of biodiesel in the glycerol-rich phase decreased, with no significant change in the binodal curves and tie-lines. We then successfully estimated the binary interaction parameters and observed that very good agreement was obtained between the experimental data and the calculated values using the UNIQUAC model, with maximum deviations of about 0.25%. We thus firmly believe that such parameters can be safely used, e.g., to design and efficiently operate separation processes for systems like the ones investigated in this article.