mazut

thumb|Russian aircraft carrier Russian aircraft carrier Admiral Kuznetsov|Admiral Kuznetsov uses mazut as a fuel, leading to a visible trail of heavy black smoke that can be seen at a great distance. Russian naval officials have said that the failure to properly preheat the mazut prior to entering the combustion chamber may contribute to the heavy smoke trail.

Mazut () is a very high-sulfur, low-quality heavy fuel oil that is typically produced as a residual product of petroleum refining after gasoline, diesel, and other light distillates are removed from crude oil. Similar to Bunker C (No. 6 fuel oil), mazut has high viscosity and sulfur content and is generally used as a fuel for large industrial boilers and power plants. However, unlike Bunker C, mazut is produced from lower grade source crude oil with higher sulfur content. Mazut is produced primarily in Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan.