TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The transesterification is carried out in presence of a base. The method further involves mixing the biofuel with a compound selected from glycerol formal, biodiesel, and/or petrol-derived diesel. Preferred Components: The oil or fat of animal or vegetable origin is selected from rapeseed oil, sunflower oil, palm oil, coconut oil, soy oil, and/or olive oil (preferably rapeseed oil). The biodiesel is selected from methyl or ethyl esters from the transesterification of rapeseed oil, sunflower oil, palm oil, coconut oil, soy oil, and/or olive oil. Preferred Biofuel: The biofuel (wt.%) contains the compounds (I) and (II) (higher than 95 wt.%). The product obtained by the method contains the biofuel (higher than 7 or higher than 40, preferably 70-85), and glycerol formal (greater than or equal to19 or greater than or equal to12, especially 15-30), respectively, biodiesel obtained from rape-seed oil (balance), petrol-derived diesel (50-95), and at least one component selected from antioxidants, agents for increasing the octane number, biocides, chelating agents, detergents, dispersants, solvents, corrosion inhibitors, oxide inhibitors, and cetane improvers. EXAMPLE - Glycerol formal esters were produced from fatty acid by transesterification of rapeseed oil with glycerol formal, as follows. A glycerol formal solution (3557.4 g) and sodium hydroxide (14.3 g) were added to rapeseed oil (262.5 g). The mixture was heated up to 70degreesC and stirred at 250 rpm for 16 hours. Subsequently, the mixture was cooled down to 30degreesC and water was added to the crude reaction until the total separation of the two layers. The polar layer was neutralized to pH 7 and the excess of glycerol formal was distilled at reduced pressure to be recycled. The fraction which was not distilled, and contained free glycerol was reacted with formaldehyde in the presence of an acid catalyst to regenerate the glycerol formal. The apolar layer (the upper layer), which contained glycerol formal ester, was separated, and washed with an aqueous solution of H2SO4 5% (312.3 ml). After, the organic layer was washed with water until the pH is 7. The product was dried with anhydrous Na2SO4, filtered off and finally, the residual water was distilled off at reduced pressure to yield glycerol formal esters of rapeseed oil fatty acids (254 g, yield = 98%). Ternary mixtures of methyl fatty ester/glycerol formal/glycerol formal ester of fatty acid of rapeseed oil, was produced using (wt.%) methyl fatty acid ester rapeseed oil (49), glycerol formal (12), and glycerol formal ester of the rapeseed fatty acid (39). The mixture was miscible both at 0degreesC and 20degreesC.