Heavy Fuel Oil

Heavy fuel oil is a high-viscosity residual bunker grade blended from refinery residue and cutter stock, requiring heating to about 40 to 50 degrees Celsius for storage and roughly 130 to 150 degrees Celsius at the engine for injection. Its grades are specified in ISO 8217, with viscosity to 700 cSt at 50 degrees Celsius. Since the 2020 cap, HFO use outside scrubber-fitted ships is limited to fuel at or below 0.50 percent sulphur. The Polar Code and a 2024 MARPOL amendment restrict carriage and use of HFO in Arctic waters because of spill and black-carbon concerns.