NOVELTY - The apparatus comprises storage vessels (OCV) for a mixture of methanol and a transesterification catalyst and for oil to be converted into biodiesel, a reactor feed vessel (RF) connected to the storage vessels, a reactor vessel that is connected to both the reactor feed vessel and the storage vessel, and a centrifugal pump (P1, P2, P3). The reactor vessel is a downflow gas contactor reactor comprising a column configured to allow a liquid input and a gas input into an upper section of the column via an orifice or nozzle. The apparatus is configured in single batch operation mode.    USE - The apparatus is useful for the production of biodiesel.    ADVANTAGE - The apparatus ensures economical, rapid and simple production of biodiesel with high ester content (94-98%), low mass transfer resistance, high product yield (95-99%), low power and energy consumptions, high conversion and less or no requirement of purification and without residual glycerol, and maximizes the range of different oils and fats as starting materials.    DETAILED DESCRIPTION - The apparatus comprises storage vessels (OCV) for a mixture of methanol and a transesterification catalyst and for oil to be converted into biodiesel, a reactor feed vessel (RF) connected to the storage vessels, a reactor vessel that is connected to both the reactor feed vessel and the storage vessel, and a centrifugal pump (P1, P2, P3). The reactor vessel is a downflow gas contactor reactor comprising a column configured to allow a liquid input and a gas input into an upper section of the column via an orifice or nozzle. The apparatus is configured in single batch operation mode, a multiple batch operation mode or a continuous mode. The orifice or nozzle is configured such that the liquid input and optionally the gas input flow downwards through the column and the turbulence and shear at the interface between the orifice or nozzle and the column results in mixing and highly efficient mass transfer. The column of the downflow gas contactor reactor has an internal diameter of 5 cm to 1.0 m, and a height of 1-25 m, and comprises a cylindrical upper section and an inverted conical lower section. The apparatus is configured such that the mixture of methanol and the transesterification catalyst are pumped directly from its storage mixture using a pump to the reactor feed vessel and the downflow gas contactor reactor. The ratio of the internal diameter of the orifice or nozzle used at the entry point of the downflow gas contactor reactor to the internal diameter of the column is 1:6-1:25. An INDEPENDENT CLAIM is included for a method for the production of biodiesel.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a batch production unit.    Mixing vessel (OCV)    Oil storage vessel (OSV)    Centrifugal pumps (P1, P2, P3)    Reactor feed vessel (RF)    Settling vessel. (SV)