With the recent introduction of stringent environmental regulations, such as those from the IMO, ship owners and operators are increasingly obliged to operate their MAN B&W two-stroke main engines on ultra-low sulphur fuels in defined marine zones. Furthermore, CARB (the Californian Air Resource Board) has enforced the use of diesel oils (MDO) or gas oils (MGO) in Californian waters since 1 July, 2009, while European harbours introduced similar requirements at the start of 2010. These new requirements ultimately mean more frequent, running changeovers in fuel type aboard marine vessels.