Fuel oil is any of various fractions obtained from the distillation of petroleum (crude oil). Such oils include distillates (the lighter fractions) and residues (the heavier fractions). Fuel oils include heavy fuel oil (bunker fuel), marine fuel oil (MFO), furnace oil (FO), gas oil (gasoil), heating oils (such as home heating oil), diesel fuel, and others.

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Oil has many uses; it heats homes and businesses and fuels trucks, ships, and some cars.

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Mazut is a residual fuel oil often derived from Russian petroleum sources and is either blended with lighter petroleum fractions or burned directly in specialized boilers and furnaces. It is also used as a petrochemical feedstock. 

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Bunker fuel or bunker crude is technically any type of fuel oil used aboard water vessels

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The term "bunkering" broadly relates to storage of petroleum products in tanks (among other, disparate meanings). The precise meaning can be further specialized depending on context. Perhaps the most common, more specialized usage refers to the practice and business of refueling ships. Bunkering operations are located at seaports, and they include the storage of bunker (ship) fuels and the provision of the fuel to vessels

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