Abstract: In order to reduce the loss of product oil during unloading in tank farm or gas station, the concerned equations must be applied correctly to enhance the tracking metering for the density of light oil unloaded besides correct installation of metering devices and meeting its operational needs, regular maintenance, calibration and proving. The density of product oil should be checked in time due to the differences of standard density among the product oils with different grades and different batches when unloading at tanks and batches changed. Temperature is also a factor influencing with the metering accuracy in unloading, so the temperature of the product oil unloaded should be correctly determined in time. The water content and impurity in the product oil not only produce wrong metering results, but also interfere with the normal operation of meters (metering distortion). It is neccessary to regularly clean tanks, dewater and deimpurity (including relay tanks). Filter must be installed ahead the flowmeter and contaminations drainage must be done regularly.