Marine gasoil (MGO) describes marine fuels that consist exclusively of distillates. Distillates are all those components of crude oil that evaporate in fractional distillation and are then condensed from the gas phase into liquid fractions. Marine gasoil usually consists of a blend of various distillates. Marine gasoil is similar to diesel fuel, but has a higher density. Unlike heavy fuel oil (HFO), marine gasoil does not have to be heated during storage.
Marine gasoil and standard heating oil largely share the same properties. Therefore, heating oil is sometimes supplied as marine fuel when there are shortages of marine gasoil according to the ISO 8217 DMA designation. However, in this case the flashpoint of the relabeled heating oil must be above 60°C, which is usually the case. Furthermore, it must be ensured that the engine technology or any installed exhaust filter systems on the ships are compatible with the relatively low sulfur content of heating oil.
MGO has a transparent to light color. If the marine fuel is used in inland waterway shipping, like heating oil it must be marked with Solvent Yellow 124 dye. In addition, the marine gasoil is colorized red. These measures are to prevent – or enable the detection of – the misuse of low-taxed and relatively cheap heating oil or marine gasoil (which is in fact often the same fuel) in inland shipping.