NOVELTY - Producing biodiesel through transesterification involves introducing multiple reactants into a reaction zone, where the reactants comprise at least feedstock oil and an alcohol; having a catalyst in the reaction zone, where the catalyst comprises a molten metal or a molten metal alloy; and reacting the multiple reactants to form biodiesel and glycerol in the reaction zone, where the reaction is catalyzed by the catalyst.    USE - For producing biodiesel through transesterification (claimed).    ADVANTAGE - The catalyst comprising tin alloys with low melting point temperatures allow for low operation temperature. The molten catalyst remains in the reaction zone and does not contaminate the product stream thereby product separation and recovery are manageable. By using molten metal catalyst it is possible to produce high quality glycerol as a second valuable product. The molten metal catalyst is readily available and inexpensive relative to other traditionally used catalysts. The tin catalyst is not deleted or deactivated during the course of reaction. The molten metal process has improvement over the traditional supercritical biodiesel production methods, as its thermodynamic reaction conditions are less severe. This allows for cost savings in thinner-walled tanks, reactors, piping and other equipments as well as savings in operating costs by requiring less energy input. The molten metal catalyst does not leave the reaction zone as the products exit from the reactor thereby making separation of products manageable. This behavior is similar to heterogeneous catalyst and is due to large density difference and immiscibility between the molten catalyst and the reactants and products in the reaction zone. Using molten metal catalyst enables a process that produces high quality glycerol. The method allows application of large alcohol ratios that provide extra product yield.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) catalyzing a transesterificaton reaction involving introducing multiple reactants into a reaction zone, where the reactants comprise a first alcohol and a first ester; having a catalyst in the reaction zone, where the catalyst comprises a molten metal or a molten metal alloy; and reacting the multiple reactants to form multiple products, where the products comprise a second alcohol and a second ester, where the second ester is different from the first ester, and the reaction is catalyzed by the catalyst; and    (2) producing an ester from a carboxylic acid involving introducing multiple reactants into a reaction zone, where the reactants comprise the carboxylic acid and an alcohol; having a catalyst in the reaction zone, where the catalyst comprises a molten metal or a molten metal alloy; and reacting the multiple reactants to form a product, where the products comprise the ester and water, and the reaction is catalyzed by the catalyst.