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The pour point is the lowest temperature at which a residual fuel can be handled without excessive amounts of wax crystals forming out of solution. If a fuel is below the pour point, wax will begin to separate out which will block filters. Wax will also build up on tank bottoms and on heating coils. When heat is re-applied it can be difficult to get the wax to re-dissolve because of its insulating nature. In extreme cases manual cleaning of tanks becomes necessary.

To avoid the operational difficulties just described, it is necessary to store the fuel at least 10°C above the pour point. The transfer pumps in the fuel system are usually designed to operate at a maximum viscosity of 800 - 1000 cSt. For efficient transfer, the fuel should therefore be heated to the right viscosity. For less viscous fuels, i.e. below IF 100, the important parameter for viscosity purposes is the pour point.

For residual fuels, the typical pour point is less than 10°C, however there are occasional instances of 35 - 40°C. The pour point is a characteristic of the crude processed and can also be affected by the manner in which the fuel is manufactured. The pour point can be simply determined although the result cannot be considered to be absolute, it will at least establish if the fuel has a high pour point.