Mazut

Mazut is a heavy, low quality fuel oil, used in power plants and similar applications. In the United States and Western Europe, by using FCC or RFCC processes, mazut is blended or broken down, with the end product being diesel. 
Mazut may be used for heating houses in the former USSR and in countries of the Far East that do not have the facilities to blend or break it down into more conventional petro-chemicals. In the West, furnaces that burn mazut are commonly called "waste oil" heaters or "waste oil" furnaces.
Mazut-100 is a fuel oil that is manufactured to GOST specifications, for example GOST 10585-75 (not active) or GOST 10585-2013 (active as per December 2019). Mazut is almost exclusively manufactured in the Russian Federation, Kazakhstan, Azerbaijan, and Turkmenistan. This product is typically used for larger boilers in producing steam since the energy value is high.
The most important factor when grading this fuel is the sulfur content, which can mostly be affected by the source feedstock. For shipment purposes, this product is considered a ”dirty oil” product, and because viscosity drastically affects whether it is able to be pumped, shipping has unique requirements. Mazut is much like Number 6 Oil (Bunker C), and is part of the products left over after gasoline and lighter components are evaporated from the crude oil.
Different types of Mazut-100.
The main difference between the different types of Mazut-100 is the content of sulphur. The grades are represented by these sulfuric levels:
Very Low Sulphur mazut is generally made from the lowest sulfur crude feedstocks. It has a very limited volume to be exported because:
Low to high sulfur mazut is available from Russia and other CIS countries (Kazakhstan, Azerbaijan, Turkmenistan). The technical specifications are represented in the same way, according to the Russian GOST standard 10585-99. The Russian origin mazut demands higher prices.