Abstract: An apparatus and method for storing and supplying a fluid for use by a motorcycle engine includes a fluid tank assembly that can be mounted so that at least a portion of it is integral with a motorcycle frame. The assembly includes a center block that is mounted within a cavity in the motorcycle frame and two fluid reservoir housings, each mounted on opposite sides of the frame exterior and adjacent to the center block. The center block includes a hole of sufficient diameter that reservoir chambers, defined by the two reservoir housings, are in a free-flowing, fluid communication with one another via the center block hole. Moreover, the center block is a structural element thereby providing strength to the motorcycle frame.