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Recently, biodiesel has become one of the most significant clean alternative biofuels because of many advantages. However, it has also some shortcomings such as: higher density and viscosity. The high density of biodiesel can cause an increase in the fuel consumption and NO_X emissions. In order to overcome this problem, the blending of biodiesel with diesel fuel or alcohols is generally recommended in the existing literature. Although many one-dimensional models are proposed by different authors for predicting fuel properties of biodiesel-diesel binary blends, two-dimensional models are still inadequate for estimating densities of biodiesel-diesel fuel-alcohol ternary blends. Therefore, in this study, (1) densities of waste cooking oil biodiesel-diesel fuel-ethanol ternary blends were measured at different temperatures (278.15  343.15 ) according to ISO test method, and (2) some two-dimensional models, previously suggested by the authors, were fitted to the density data of ternary blends obtained from the authors and specialized literature to determine the best correlation for prediction of density. The quadratic surface model is found to be best predictor to estimate densities of ternary blends.