Abstract: In a first aspect, systems and methods for producing biodiesel fuel include a modular production unit incorporated onto a single platform or into a housing for ease of relocatability. The modular production unit preferably includes a mixing unit, a reaction chamber, a separation unit, a filtering unit, all incorporated onto or into a self-contained platform or housing that is able to be easily relocated. In a second aspect, the modular production unit is combined with additional fixed and/or relocatable components to provide a biodiesel processing plant.