Abstract: In international petroleum trade, during purchase and transfer from an intermediate terminal of petroleum products, petroleum loss may occur. Besides, there are differences between trading countries/regions in integrity, modes of metering/delivery, units of measurement, hardware conditions, as well as interpretation and implementation of measurement standards. In this paper, major controlling factors for such losses are identified in three processes, namely, loading at the departure port, transportation and discharging at the destination. In the loading process, the density, temperature and volume of petroleum are major factors; in the ship transportation process, volume table, ship metering and fluctuations of sea level are major factors; in the discharging process, petroleum density of ashore tanks, volume and temperature of recovery petroleum are major factors. Proper control measures are proposed to minimize such losses from the source. Application of these measures may minimize losses in petroleum purchase and the research result has practical significance for guaranteeing the economic benefit of enterprises.