This invention discloses a reaction system for producing fatty-acid alkyl esters using liquid film reactors, with countercurrent flow scheme based on the alcoholysis of fats and oils. Reaction system comprises a descending film reactor using semi-structured packing for generating interfacial area. It is fed through the bottom with oil or fat, and with a mixture containing alcohol, glycerol and catalyst through an intermediate stage. Products are a mixture of fatty-acid alkyl esters, alcohol and catalyst and alcohol, glycerol and catalyst, exit via the top and the bottom of the reactor, respectively. Volumetric packing fraction is between 2% and 50%, reaction temperature from 25 to 180° C., molar ratio alcohol to oil between 3:1 and 10:1, and CH3OH, NaOH, KOH, or their mixtures (0.5% to 3% based on the oil mass flow rate). Conversion and yield in a single reaction step are greater than 99.7% and 99.9%, respectively.