Custody transfer of ownership of Fuel Oil demand for a small level of uncertainty to prevent a significant loss of revenue. Local national or international Wheigh & Measure standard drives the selection of primary flow element (including Ultrasonic, Turbine, Orifice, Positive Displacement), the number of runs, the lay out, the instrumentation & control and the proving system. The optimal design results into the best solution to allow better quality, safety, accuracy and performance while minimizing the fabrication, trasportation, installation and ownership cost.