Studying alternative raw materials for biodiesel production is of major importance. The use of mixtures, namely, by incorporating wastes, is an environmental friendly alternative and might reduce production costs. The objective of the present work was (i) to study biodiesel production using vegetable oils (virgin and waste) mixed with animal fat, (ii) to analyze the variations in biodiesel composition, aiming its prediction when mixtures with different fat contents are used as raw materials, and (iii) to understand how mixture composition influences biodiesel quality. Production yields varyed from 81.7 to 88.8 wt %; furthermore, the obtained products fulfilled most of the determined quality specifications according to European biodiesel quality standard EN 14214. Minimum purity was only achieved using waste frying oil or soybean oil alone as raw material; however, it ranged from 93.9 to 96.6 wt %, always being close to the limit (96.5 wt %). It was possible to establish a model to be used for predicting composition and some parameters of biodiesel resulting from the mixtures, and it could be estimated that the use of at least 12% lard in a soybean oil/lard mixture would be effective in reducing the iodine value of biodiesel to acceptable values. Considering the use of virgin or waste vegetable oils, it was concluded that waste frying oil might be an alternative raw material to obtain a biodiesel fulfilling European standard at a lower cost.