No. 6 Fuel Oil (Bunker C) is a heavyweight material that is difficult to pump and requires pre-heating for use. This fuel oil may be heavier than water, is not likely to dissolve, is difficult or impossible to disperse, and is likely to form tar balls, lumps, and emulsions. It has a low volatility and moderate flash point.
More Number 6 oil is produced compared to Number 5 oil, the terms heavy fuel oil and residual fuel oil are sometimes used as names for Number 6. Number 5 and 6 are what remains of crude oil after gasoline and the distillate fuel oils are extracted through distillation. Number 6 oil may also contain a small amount of No. 2 to get it to meet specifications.
Bunker C 