NOVELTY - Preparing (P1) a fatty acid alkyl ester from a feedstock involves providing a feedstock containing at least one source of fatty acids; mixing the feedstock with a treatment composition containing alcohol and a catalyst to form a reaction mixture (10); forcing the reaction mixture through at least two controlled flow cavitation apparatuses (12) at a processing pressure capable of generating a hydrodynamic cavitation zone in each the controlled flow cavitation apparatus, maintaining a pressure differential across each the controlled flow cavitation apparatus is 30-500 psi.    USE - For preparing fatty acid alkyl ester (claimed) use as biodiesel.    ADVANTAGE - The method increases mixing efficiency, decreases reaction time, increases the conversion rate i.e. 95 (preferably 98)%, and reduces production costs.    DETAILED DESCRIPTION - Preparing (P1) a fatty acid alkyl ester from a feedstock involves providing a feedstock containing at least one source of fatty acids; mixing the feedstock with a treatment composition containing alcohol and a catalyst to form a reaction mixture, where the temperature of the reaction mixture (10) is 40-200 degrees C; forcing the reaction mixture through at least two controlled flow cavitation apparatuses (12) at a processing pressure capable of generating a hydrodynamic cavitation zone in each the controlled flow cavitation apparatus, maintaining a pressure differential across each the controlled flow cavitation apparatus is 30-500 psi, where at least one of the fatty acids is converted into a fatty acid alkyl ester. An INDEPENDENT CLAIM is included for increasing (P2) the conversion rate of fatty acid to fatty acid alkyl ester involving combining a feedstock containing fatty acids with an alcohol and a catalyst to form a reaction mixture, where the temperature of the reaction mixture is 40-200 degrees C; and passing the reaction mixture through at least two controlled flow cavitation apparatuses, where the conversion rate of fatty acids in the reaction mixture to fatty acid alkyl esters is greater than 90%.    DESCRIPTION OF DRAWING(S) - The figure shows cross section view of controlled flow cavitation apparatus.    Reaction mixture (10)    Two controlled flow cavitation apparatuses (12)    Flow-through channel (20)    Localized flow constriction (21)    Orifices (22)