Tricks of the Bunker Trade: Understanding the Fuel Density & Weight Relationship

Marine fuel is always sold by weight (mass) and delivered by volume. Hence for this reason bunker receipts must always be signed "For Volume Only" and adding the words "weight to be determined after testing of the representative sample".

Never sign for weight if uncertain about the density.

What many bunker surveyors do not realise is that the density given in the supplier's bunker delivery note (BDN) may not be true and thus the weight determined by calculation should be considered as the 'preliminary' weight of the fuel transferred to the vessel.

The actual weight is only determined after the density is verified by an independent fuel testing authority and then factored into the final recalculation of the actual weight of the fuel delivered onboard.

That is why we always stress the importance of accurately obtaining bunker samples both onboard the vessel and the barge.

Once the samples are dispatched to the vessel's chosen independent fuel testing laboratory we request the copy of the Fuel Test Reports so that revised bunker survey report can be sent to the client.

This procedure assists our clients in avoiding commercial losses. Below is a typical scenario of how density can affect the weight of fuel transferred on board.

A ship owner/charterer has a fleet of 20 vessels bunkering an average of 1000 MT each month.

Now imagine a charterer operating a fleet of 50, 70 or 100 vessels – the commercial loss would be valued in millions of dollars every year!

Key Notes

• If the density of fuel cannot be verified onboard or independently verified at the time of bunkering, the BDN should be signed only for 'volume' and not for weight
• Remember whenever in doubt or have concerns always issue a letter of protest

Kaivan H. Chinoy is the Founder and Principal Marine Surveyor of AVA Marine Group, owners of Petro Inspect and The Bunker Detectives.