In this work, studies of the transesterification using sodium hydroxide as a catalyst of mixtures of soybean oil/coconut oil (SO/CNO) and soybean oil/castor oil (SO/CO) before and after interesterification (in the presence of potassium methoxide as a catalyst) are presented. To the best of our knowledge, studies comparing raw materials from different sources to the same fatty acid composition have not been carried out. The results point out that the SO/CNO transesterification of mixtures, before and after interesterification, results in a slight difference in the profile of alcoholysis; i.e., if the fatty acid composition is known, it is possible to envisage the kinetic behavior of the reaction, at least for triacylglycerols of oils or fats with an usual fatty acid composition. On the other hand, in the case of the presence of castor oil, transesterification also occurs during interesterification, with the ricinoleate moiety acting as a transesterification agent as a result of the presence of the hydroxyl group at C12. Therefore, the formation of estolides that exhibit high viscosity is observed, and from C-13 nuclear magnetic resonance, it is possible to estimate the degree of esterification of the C12-OH group (90% for the SO/CO mixture and approximately 70% for neat CO). As a result of this fact, the relative rate of transesterification of the interesterified SO/CO mixture is lower than that of the physical mixture.