Binodal curves of systems involved in the production of soybean oil biodiesel and castor oil biodiesel were obtained at different temperatures by the titration method under isothermal conditions. The measurements allow the analysis of the mutual solubility of the compounds present after the transesterification reaction and supply data for the process of separation and purification of biodiesel. The systems studied were soybean oil biodiesel + glycerol + ethanol at temperatures of (298.15, 333.15, and 343.15) K, soybean oil biodiesel + ethanol + water at temperatures of (298.15 and 323.15) K, and castor oil biodiesel + ethanol + glycerol to 333.15 K. The highest levels of biodiesel were obtained at 298.15 K, although small changes in temperature did not significantly affect the system behavior. The two-phase region for the system of ethanol + biodiesel + glycerol at 333.15 K using soybean oil as raw material was bigger than the two-phase region using castor oil, which allows us to separate higher amounts of biodiesel after the transesterification reaction at the stage of interest.