Urea complexation is a fractionating process to separate poly unsaturated fatty acids from vegetable and animal oil, based on the capability of saturated fatty acids (SFAs) to form complexes with urea in the ethanolic solution, which generates a solid-liquid system. This research determined models which are suitable for the fatty acid, urea, and ethanol/methanol solid-liquid equilibrium. Furthermore, activity coefficients and interaction parameters between the substances involved were evaluated. Pure SFAs were used in this experiment instead of SFAs produced from vegetable oil saponification. Solid-liquid phase diagrams for binary and ternary saturated fatty acid-urea-ethanol were developed. These binary data were used to determine experimental activity coefficients and interaction parameters using thermodynamic models based on excess Gibbs free energy, such as Wohl, Wilson, Margules, and nonrandom two liquid models. The resulting interaction parameters gave a good fitting between experimental data and adjustable or predictive models.