Intermediate Fuel Oil

Intermediate Fuel Oil is a blend of heavy residual oil and distillate cutter stock, standardised to ISO 8217 at viscosities of 180 cSt or 380 cSt at 50 °C, and historically the dominant main-engine bunker fuel on ocean trades. Despite its lower cost compared with distillate fuels, IFO requires extensive pre-treatment: centrifugal purifiers remove water and catalytic fines, and heaters bring viscosity down to between 12 and 17 cSt before injection. Catalytic fines — residues of fluid catalytic cracking — are particularly damaging to fuel injection equipment if not reduced below 60 mg/kg through effective purification. Since January 2020 the sulphur cap in MARPOL Annex VI Regulation 14 has limited the global use of IFO above 0.50% m/m sulphur unless the vessel is fitted with an approved exhaust gas cleaning system. Operators who retain high-sulphur IFO for scrubber-fitted vessels must document fuel segregation carefully in the Oil Record Book and Bunker Delivery Notes to demonstrate compliance. MEPC.1/Circ.795 provides guidance on consistent implementation of the global cap.