Abstract: Mass metering of crude oil is used in the main delivery station in the Daqing oil field.A eomplete outfit of high accuracy metering instruments was developed in 1975 and,after two odd years of trial,was certified in 1977 by the National Bureau of Metering Standards as qualified for useplcommervial settlements.In this outfit,standard volumetric-tube real-liquid calibrated flowmeter and Roots flowmeter are used for metering crude oil volume,dual-tube vibration density meter for measuring crude oil density,low water content analyser for measuring percentage of water content of crude ail in volume,and equipped with volume-mass flow accumulator and computer,the outfit can be used to xead out total volume,net weight,water content,average percentage of water content and average density of crude oil passing through the metering station.The instruments are of high accuracy,with ±0.006% reproducibility of the standard volumetric tube,accuracy of the Roots flowmeters higher than ±0.2%( 54.5% of the flowmeters with accuracy up to ±0.1%),absolute error of dual tube vibration density meter Iess than 0.001g/cm³,absolute error of low water content analyser less than ±0.1%.