Mazut-100 and the economics of the heavy end

Every barrel of crude has a bottom, the dense, dark residue left after the lighter, more valuable fractions have boiled away. Mazut-100 is that residue graded and sold. It is not glamorous, it prices at a discount to the products above it, and it still moves in enormous volume. Understanding the heavy end is understanding where a refinery makes or loses its last few dollars.

What sits at the bottom of the barrel

When crude is distilled, the tower separates it by weight. Gases and petrol come off the top, kerosene and diesel in the middle, and what remains at the base is the residual fraction. Mazut is that heavy residual fuel oil, thick enough that it often has to be heated before it will even pour. Its energy content is high, but so is its density, its viscosity, and the concentration of everything the lighter cuts left behind, from sulphur to metals.

Because it is a residue, its value is set by what the market above it will pay. A refinery that can crack the bottom of the barrel into more diesel will do so whenever the margin justifies it. What is sold as Mazut is, in part, the volume that was not worth upgrading at that moment, which is exactly why its price tracks the spread between heavy and light products.

Grades, sulphur, and GOST 10585

Mazut is graded under the Russian and CIS standard GOST 10585, and the grade names describe the fuel with precision. Mazut-100 refers to a viscosity grade, and the specification is further split by sulphur content into low, medium, and high sulphur bands. Sulphur is the number buyers watch first, because it determines both the environmental limits on burning the fuel and the discount it trades at.

Viscosity, pour point, flash point, and ash and water content fill out the sheet. A buyer for a power station and a buyer for a marine blender are reading the same specification for different reasons, one focused on how the fuel burns in a boiler, the other on how it blends toward a bunker grade. The grade is a shorthand, and the certificate of analysis is where the real quality is proven.

• Mazut-100 names a viscosity grade, then splits by low, medium, and high sulphur bands.
• Sulphur content drives both the regulatory ceiling on burning it and the price discount.
• Pour point matters because the fuel is thick and often must be heated to move at all.

The heavy end is where a refinery margin is decided, one grade and one sulphur band at a time.

Where the demand still is

For all the talk of its decline, the heavy end still has buyers. Power generation in markets that run oil-fired plants remains a steady outlet, particularly where gas is scarce or expensive. Industrial heat, from cement to large boilers, takes another share. And the marine sector, reshaped by the 2020 sulphur cap, still draws on residual streams that are blended down into compliant fuel.

For a trader the heavy end is a spread business. The money is in reading the gap between crude and product, between high and low sulphur, and between one region surplus and another shortage. It rewards patience and storage as much as movement. Mazut will not headline anyone slate, but it clears in size, it prices off a logic you can follow, and it keeps the bottom of the barrel liquid.