Comtrade tries to estimate quantity or netweight only if country does not report them. That is the reason why unit value varies between reporting countries (or even within the same reporting country; depends on trade flow, partner country, etc).

 At part of estimation procedure, Comtrade may use Standard Unit Value (SUV; generated from historical data) to estimate quantity/netweight.

 The following SUV are used for Imports (netweight):

code year SUV ($/kg)
33101 2004 0.2708
33101 2005 0.2708
33101 2006 0.2708
33101 2007 0.4732

For an example, if country reports import of Crude Petroleum for $500000 in 2007, but it does not report netweight, Comtrade will estimate netweight with the following calculation 5000000 / 0.4732  = 10566356 kg