Iran Strait of Hormuz: The Rise of the ‘Dark Fleet’ & Oil Tanker Crisis

The already strained flow of oil through the Strait of Hormuz is increasingly dominated by a “shadow fleet” of tankers operating outside of standard international regulations, a trend accelerated by recent attacks on shipping and escalating geopolitical tensions. Even as many vessels remain stranded awaiting safe passage, those still transiting the critical waterway are often skirting rules related to sanctions, pollution, and transparency, raising concerns about the integrity of global oil supply chains.

Iran has directly threatened to destroy ships attempting to navigate the strait, a vital chokepoint connecting the Persian Gulf to the Arabian Sea and, world markets. This, coupled with the risk of broader regional conflict, has led to a surge in insurance costs and prompted some crews to refuse voyages through the area. As of March 6, over 400 tankers were reportedly stuck in the Persian Gulf, awaiting direction from their owners.

The Rise of the “Dark Fleet”

However, a significant number of vessels continue to move through the Strait, and these are largely the ones operating under the radar. Maritime industry professionals refer to these as the “shadow fleet” – ships that deliberately avoid scrutiny by ignoring international restrictions, violating environmental regulations, or concealing their cargo and activities. The existence of this fleet isn’t latest, but its prominence is growing as legitimate shippers face increased risks and costs.

The fundamental challenge lies in the voluntary nature of international maritime regulation. While the International Convention for the Safety of Life at Sea (SOLAS) requires most commercial vessels to broadcast their identity, position, speed, and heading via a radio transponder (AIS), there’s no enforcement mechanism to prevent crews from simply switching these transponders off or transmitting false information. When a ship “goes dark,” it disappears from tracking maps without triggering any global alert. There is no central maritime authority overseeing compliance.

National jurisdiction adds another layer of complexity. Every vessel sails under a flag, theoretically making its country of registration responsible for regulation and inspection. In practice, however, ship registration has become a commercial transaction. Companies can register vessels in countries like Cameroon, Palau, or Liberia – and even landlocked Mongolia – often for minimal cost and with limited oversight. A ship can even change flags if it comes under scrutiny, and some registries offer online registration, potentially allowing vessels to operate without any legitimate oversight.

Insurance: The Thin Line of Enforcement

Insurance represents the closest thing to a real enforcement mechanism in the maritime world. Reputable insurers, largely based in London, require vessels to meet safety standards, carry proper documentation, and comply with international trade sanctions. Without insurance, ships struggle to enter major ports or secure cargo contracts. However, this system is similarly being circumvented. According to reports, as much as two-thirds of ships carrying Russian oil – trade restricted by the U.S. And other nations – have “unknown” insurance providers, leaving questions about who would cover the costs of a spill or collision. This allows ship owners to opt out of the established system entirely, utilizing less reputable ports or conducting ship-to-ship transfers at sea.

The case of the tanker Skipper illustrates this point. The United States seized the vessel in December 2025, despite the fact that Guyana, under whose flag it was sailing, had never actually registered it. The ship was, in effect, stateless.

Techniques for Obfuscation

The methods employed by the shadow fleet are increasingly sophisticated. Vessels have been found to change their International Maritime Organization (IMO) identification numbers – a unique code assigned to every ship, akin to a vehicle identification number (VIN) on a car. A common tactic involves purchasing aging tankers destined for scrap, registering them through shell companies, obtaining flags of convenience, securing opaque insurance, and then switching off transponders when approaching sensitive areas. Cargo is often transferred ship-to-ship on the open ocean to further obscure its origin and destination. If a vessel attracts unwanted attention, it can simply change its name and re-register under a different flag, starting the process anew.

Maritime intelligence firm Windward estimates that approximately 1,100 vessels currently operate within this “dark fleet,” representing 17-18% of all tankers carrying liquid cargo, primarily oil.

A System Built on Voluntary Participation

The emergence of the shadow fleet isn’t a sign of a broken system, but rather a revelation of its inherent nature. For decades, the maritime system functioned because opting out was more costly than complying. However, international sanctions have altered this equation, making compliance prohibitively expensive and politically damaging for some. Countries reliant on oil exports have begun building parallel systems to circumvent restrictions. Iran initiated this process in 2018 following the reimposition of sanctions, and Russia dramatically expanded it in 2022 after its invasion of Ukraine.

Now, with the Strait of Hormuz effectively closed to legitimate trade, the vessels still moving are those willing to disregard the rules. Recent reports indicate ships are turning off their AIS to evade tracking, and more companies may follow the example of Greek firm Dynacom in running the strait despite the risks.

Implications for Global Trade

The growth of the shadow fleet isn’t simply a matter of regulatory evasion; it has broader implications for global trade and security. It undermines the effectiveness of sanctions, creates opportunities for illicit activities, and increases the risk of environmental disasters. The fact that a significant portion of oil continues to flow despite the disruptions suggests a fundamental shift in the willingness to adhere to established norms. This sends a signal to those still operating within the rules: opting out may be a viable, and increasingly attractive, option.

The situation highlights the limitations of a system built on voluntary participation. While a complete overhaul of maritime regulations may be unrealistic, increased international cooperation and stricter enforcement are crucial to address the growing threat posed by the shadow fleet. The current crisis in the Strait of Hormuz serves as a stark reminder that the rules of the sea are only as strong as the collective will to enforce them.