Marine diesel oil (MDO)

Marine diesel oil (MDO) is the trade name for the ISO 8217 grades DMB and DFB, distillate fuels that permit a small residual content and are therefore heavier, more viscous and more variable than the DMA and DMZ grades sold as marine gas oil. ISO 8217:2024 Table 1 sets DMB at 2.000 to 11.00 mm2/s at 40 degrees C, a maximum density of 900.0 kg/m3 at 15 degrees C and a minimum cetane index of 35.0.

The full article will explain what the residual fraction does to the fuel: the existent total sediment and water characteristics that DMA does not carry, the clear-and-bright condition that decides whether those tests are required at all, and the purification the grade needs that a pure distillate does not. It will also address the naming confusion that surrounds the term, since MDO, DMB and the older IF grades are used interchangeably in the market and in charter party bunker clauses without meaning the same thing.

MDO’s commercial position is narrowing. Engine builders classify DMB separately from MGO in their fuel guidance, ECA trading pushes buyers toward pure distillate, and the 2024 edition of ISO 8217 added the bio-blend grade DFB alongside it. The article will say where DMB is still bought and why.