Mass flow meters are deployed for metering of heavy hydrocarbon such as bunker fuels. There are many challenges in measurement of mass flow influenced by high viscosity and multiphase fluids. National Metrology Centre developed a primary liquid flow standard which is capable to perform water and high viscous fluid calibration from 0.8 to 80 M3/h using gravimetric method which can calibrate mass flow meters two phase flow conditions in range of 0 to 30% gas-oil volume ratio with measurement uncertainties range of 0.05 % to 0.2 %.