The present invention provides a method and apparatus for reacting a natural oil with a short chain alcohol in the presence of alkaline catalyst, in which a mixture of natural oil, short chain alcohol and alkaline catalyst is fed in one direction along a pipe reactor under transitional or turbulent conditions, so that the reactants are mixed in a direction normal to the flow direction to a greater degree than in a direction parallel to the flow direction or so that the reactants are mixed in a direction normal to the flow direction, such that the time taken for 90% of the elements of fluid to pass through the reactor is within 20% of the mean residence time of reactant in the reactor. There is also provided a ship, comprising means for storing a raw material used in the synthesis of biodiesel, a plant for the synthesis of biodiesel and means for storing the biodiesel synthesized.