Biodiesel is currently produced from a catalytic transesterification reaction of edible and nonedible oils with methanol. New policies are encouraging the development of advanced biofuels produced from lignocellulosic feedstocks or industrial waste as animal fat. This material is less expensive than current oils but usually has high content of free fatty acids and a pre-esterification reaction becomes necessary, increasing the cost of the catalytic process. The production of biodiesel using supercritical alcohols is appropriate for materials with high acidity and water content; therefore, the use of this method for animal fat is a promising alternative. Two different processes have been studied: a single-step direct transesterification using supercritical ethanol and a two-step process of hydrolysis and esterification. Ethanol, instead of methanol, has been used as the reagent because it can be produced from biomass via fermentation, resulting in a complete renewable biofuel. The final conversion and degradation of unsaturated fatty acid esters, which is the main drawback of these high temperature and pressure processes, have been studied through the change of several parameters such as temperature, ethanol:animal fat molar ratio, and reaction time.