The residues that make up residual fuels come from several refinery processes.

Fuels are classified to an international standard known as ISO8217:1996 There are four grades of distillate fuels and 10 grades of residual fuels.

A bunkering operation involves most  sections of the ISM code, esp. section 7 relating to procedures for the prevention of pollution.

If there is a dispute over the quantity of fuel delivered, it is not sufficient to record a quantity difference on the bunker receipt.

When taking bunkers, a representative sample of the fuel oil delivered should be given to the ship by the supplier.

Before taking on bunkers it is advisable to take a sample from the suppliers tanks and test it for stability and compatibility. Further testes are made for viscosity, density, water content etc.

As the density of the oil approaches that of water, the gravity disc, which is the method used to maintain the oil/water interface, as in a LO purifier, will no longer maintain a water seal.

A homogeniser is a piece if mechanical equipment which reduces the fuel oil particle size and evenly distributes them

For correct atomisation in the cylinder, the fuel must be at the correct viscosity.

Fuel to be used is first transferred from storage tanks to a settling tank in which it is heated to allow some water and sludge to settle out by gravity and be drained off.