During processing in the conversion units of the refinery (FCCU, hydrocracker, etc.) the stocks expand in volume due to reduction in density, resulting in volume gain or negative loss. A situation can arise in which the DOP of one participant shows volume gain (negative loss) while the other participant s DOP shows a positive loss. The allocation of actual refinery losses on the basis of retrospective DOPs becomes unrealistic, as the following example shows:

• Retrospective DOP loss, AOC= ?5,000

• Retrospective DOP loss, BOC=9,600

• Total refinery retrospective losses=4,600

• Actual refinery losses=30,000

• Loss delta=25,400

Splitting the loss delta in the ratio of retrospective DOP losses yields the following results:

• AOC delta= ?27,607 bbl

• BOC delta=53,007 bbl

• Total retrospective delta=25,400 bbl

• AOC allocated losses= ?32,607 bbl

• BOC allocated losses=62,607 bbl

• Total refinery losses=30,000 bbl

This allocation is unrealistic. Therefore, to make the losses positive in both retrospective DOPs, the balancing-grade production of each is reduced by 0.6 vol%. The actual refinery losses are next allocated in the ratio of the revised retrospective DOPs, after deducting 0.6% from balancing-grade production volumes.

The figure of 0.6%, which roughly represents unaccounted losses of the refinery during crude processing, is chosen to make the losses positive in both retrospective DOPs or, in other words, a little more than the volume gain encountered in the retrospective DOPs.