Higher viscosity bunker fuels do not automatically contain more harmful elements than lighter ones, according to ExxonMobil Marine Fuels (EMMF), which has recently been supplying 500 centiStokes fuel in response to customer demand. Emphasizing that quality and safety must be prime considerations with all fuel supplied, irrespective of viscosity, EMMF says the two crucial prerequisites for using 500 cSt fuel are the ability to heat it to a sufficiently high temperature to inject it into the vessels' engines, and the provision of purification equipment able to deal with the higher specific gravity of the product. The fuel must be maintained above its minimum pumping viscosity while in storage awaiting use.