TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In step (b), the phase containing the mixtures of fatty acid alkyl esters and the excess amount of lower alcohols or bioalcohols is optionally subjected to a further separation treatment for separating alcohols or bioalcohols (0-100%) present after step (b), and the whole excess quantity of lower alcohols or bioalcohols is kept in the final product. After step (b), an additional amount of lower alcohols or bioalcohols is added to the phase containing the mixtures of fatty acid alkyl esters and the excess lower alcohols or bioalcohols. In step (a), the transesterification is carried out with an alkaline catalyst, in three consecutive stages in which the alcohols or bioalcohols and the catalyst are dosed and recycled at every stage. The preliminary treatment of depuration of raw vegetable oil involves centrifugation, filtration, demucilagination, neutralization and wintering operations. Preferred Components: The lower alcohols or bioalcohols are selected from methanol, ethanol, biomethanol and/or bioethanol. Preferred Mixture: The amount of lower alcohols or bioalcohols (II) corresponds to an excess alcohol or bioalcohol initially present in the transesterification process. The amount of lower alcohols or bioalcohols (II) is greater than an excess alcohol or bioalcohol initially present in the transesterification process, and is obtainable in the mixture by addition after the transesterification process. The amount of lower alcohols or bioalcohols (II) is smaller than an excess alcohol or bioalcohol initially present in the transesterification process. EXAMPLE - A bio-oil (test) (1000 kg) was prepared using (kg) biomethanol (0-450), methanol (0-450), bioethanol (0-450), ethanol (0-450), sodium methacrylate (5-10.5), citric acid (0.5-1.5), sulfuric acid (0.5-1.7), hydrogen chloride (13-15.5), phosphoric acid (1.5-3) and caustic soda (10.5-13.7). A conventional biodiesel was used as control. Both test/control were evaluated for their sulfur content, carbonious residue and total solid contaminants. Results showed that test/control had sulfur content of less than or equal to 10/10, carbonious residue of less than or equal to 0.3/0.3 and total solid contaminants of less than or equal to 20/24 respectively.