The invention provides a method of reducing the soot loading of lubricating oil of a CI engine relative to a CI engine operated using a crude derived fuel, said method including combusting a low aromatics LTFT fuel under CI engine operating conditions thereby to obtain a soot loading of at least 30 mass% less over a distance of at least 4000 km than that expected under similar operating conditions when combusting a crude derived fuel. The invention extends to the use of the fuel in a CI engine.
