Satellite images show the tanker Caroline Bezengi leaking oil and sinking off the coast of Oman, with the leak reportedly reaching the shore of Al-Qibliyah Island. The vessel was carrying around one million barrels of oil. It is British-sanctioned, and is believed to belong to what is usually called the Russian shadow fleet.

That phrase appears constantly in coverage of sanctions and rarely gets explained. Here is what it means.

What a shadow fleet is

A shadow fleet — sometimes called a dark or grey fleet — is a collection of ageing tankers used to move oil in ways that avoid sanctions and the scrutiny that normally comes with international shipping.

These are not secret vessels. They are ordinary ships arranged so that no one who could be held responsible is easy to identify.

How the arrangement works

Four elements do most of the work.

• Ownership through shell companies. A ship is owned by a company that exists only on paper, often in a jurisdiction that does not publish who controls it, and it may be sold repeatedly between such companies.
• Flags of convenience. Every ship registers under a country’s flag, and that country is responsible for inspecting it. Some registries are far less demanding than others, and vessels reflag when convenient.
• Obscure or absent insurance. Mainstream marine insurers will not cover sanctioned cargo, so these ships carry cover from unknown providers — or effectively none.
• Old ships. Vessels near the end of their working life are cheap. If one is lost or seized, the loss is affordable.

Cargo is often transferred between ships at sea rather than in port, which breaks the paper trail between where oil came from and where it arrives.

How ships are meant to be tracked

Large vessels are required to carry a transponder that continuously broadcasts identity, position, course and speed. The system exists chiefly to prevent collisions, and its signals are picked up by coastal stations and satellites, which is how public ship-tracking maps are built.

Shadow-fleet vessels interfere with this in several ways. The simplest is switching the transponder off — sometimes called going dark — which is permitted only where a master judges it necessary for the ship’s safety, and is routinely misused. More sophisticated methods involve broadcasting a false position, or adopting the identity of a different vessel entirely.

Investigators therefore rely on other evidence: satellite radar and optical imagery that see a ship whether or not it is broadcasting, and the tell-tale pattern of two vessels sitting alongside each other in open water for hours, which is what a cargo transfer looks like from orbit.

None of this is exotic. It is simply expensive and slow, which is the advantage the practice relies on.

Why nobody is clearly responsible

Ordinary shipping has a chain of accountability. An owner is identifiable and insured. A flag state inspects the vessel and answers for it. A classification society certifies that the hull and machinery meet standards. Port authorities inspect vessels calling at their harbours.

A shadow-fleet arrangement weakens every link in that chain at once. The owner is a company with no assets beyond the ship. The flag state may have little inspection capacity. Certification may come from a body with lax standards, or may have lapsed. And a vessel that stays out of well-regulated ports avoids inspection altogether.

When something then goes wrong, there is often no solvent party to pursue, and coastal states discover that the international compensation system they were relying on has nothing to act against.

The crews occupy the worst position of all. They are frequently from countries with little diplomatic leverage, may be unaware of a vessel’s status when they sign on, and can find themselves aboard a detained or abandoned ship with unpaid wages and no way home.

Why it becomes an environmental problem

Every feature that makes a shadow-fleet ship useful for evading sanctions also makes it more likely to spill oil, and harder to deal with when it does.

Old vessels with reduced maintenance fail more often. Inspection under a permissive flag catches less. And when a ship does get into trouble, the normal machinery for responding depends on things a shadow-fleet vessel is designed not to have: a reachable owner, a real insurer, and a flag state prepared to act.

Under the international system, cleanup and compensation are supposed to be funded by the shipowner’s insurance. When ownership runs through shell companies and the insurer cannot be identified, the cost tends to land on whichever coastal state is nearest — which is rarely a state that had any part in the trade.

What a million barrels means

One million barrels is roughly 160 million litres. How much reaches the sea depends on how the hull fails and whether any of the cargo can be pumped off before it does.

Oil reaching an island shoreline is a particular problem. Coastlines with shallow water, reefs and mangroves are difficult to clean, and the damage to fisheries and habitat can persist for years after the visible slick has gone.

The wider point

Sanctions are designed to reduce the revenue a state earns from selling oil. One predictable response is a trade that runs outside the ordinary rules — and outside those rules sit the safety standards, inspections and liability arrangements built up over decades precisely to prevent spills.

The consequence is borne by countries with no stake in the dispute. In this case, that is Oman’s coastline.

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Sources: Associated Press; Arab News; Wikipedia Portal: Current Events, 8 August 2026.