NOVELTY - Preparing biofuel with global content of glycerol formal monoesters of (greater than or equal to85 wt.%), involves: carrying out transesterification between triglycerides of oil or fat of animal or vegetable origin, and glycerol formal, in presence of an acid or base, and removing lower layer from upper layer which is biofuel; or submitting triglycerides of oil or fat of animal or vegetable origin to hydrolysis to generate fatty acids and glycerol, followed by esterification of fatty acids obtained with glycerol formal, in presence of an acid or base catalyst.    USE - As a biofuel (claimed).    ADVANTAGE - This method provides preparation of new biofuels comprising glycerol formal in its composition (obtained by acetalization of glycerol with formaldehyde), and allows use of the total amount of glycerol obtained as by-product in the current process of manufacturing biodiesel. The biofuel produced contains has a global content of glycerol formal esters of formulae (I) and (II) (greater than or equal to85, preferably greater than or equal to95) wt.%. The transesterification of triglycerides, of animal or vegetable origin, with glycerol formal gives glycerol formal monoesters of fatty acids with high yields of (greater than or equal to85 wt.%). Thus, provides optimum technical, economical, and strategic solution to the glycerol overstock problem. The biofuels produced using the glycerol formal allow to incorporate a glycerol in a concentration of (greater than or equal to20 wt.%), keeping the good properties of the biofuels for engines, specially at low temperature. The glycerol formal esters of the fatty acids show good properties as biofuels, such as the biofuels obtained by the transesterification of rapeseed oil have a high cetane number, 60.7, which improves the performances of the biofuel in the engine. Further, the biofuel is biodegradable and has a high mass percentage derived from the renewable raw materials. The new biofuel compositions can be prepared by combining glycerol formal esters with glycerol formal, biodiesel, and/or petrol-derived diesel. Thus, it is possible to prepare binary, ternary, and even quaternary mixtures containing a high proportion of glycerol formal esters. In the binary mixtures; the glycerol formal esters can be mixed in any proportion with glycerol formal, biodiesel, or petrol-derived diesel; and the resulting biofuel formulation benefits from the unique properties of the glycerol formal ester derivatives i.e. on one hand a high glycerol content, and on the other hand, the cetane number is improved. In the ternary mixtures; the glycerol formal esters allow glycerol formal to be soluble in methyl or ethyl fatty acid esters (biodiesel) when added to a binary mixture, even when the glycerol formal is in a proportion of (one half0 wt.%).    DETAILED DESCRIPTION - Preparation of a biofuel with a global content of glycerol formal monoesters of formulae (I) and (II) of (greater than or equal to85 wt.%), involves:    (1) method (A): (a) carrying out transesterification between triglycerides of an oil or fat of animal or vegetable origin, and glycerol formal, in the presence of an acid or base, (b) removing the lower layer from the upper layer which is the biofuel, and (c) optionally washing the biofuel obtained in the step (b) with water, and drying; or    (2) method (B): submitting triglycerides of an oil or fat of animal or vegetable origin to hydrolysis to generate fatty acids and glycerol, followed by esterification of the fatty acids obtained with glycerol formal, in the presence of an acid or base catalyst.    R=alkyl chain from a fatty acid.