The Hormuz Crisis Has Made the Shadow Fleet the World’s Tanker Fleet

The Ocean Foundation Calls for Immediate IMO Emergency Response as Closure of Hormuz and Suez Routes Concentrates Global Oil Transport in Uninsured, Aging Vessels

WASHINGTON, D.C. — The Ocean Foundation today asked member states to call for an emergency session of the International Maritime Organization’s Marine Environment Protection Committee (MEPC) in response to a maritime environmental crisis unfolding in real time. The effective closure of the Strait of Hormuz — through which approximately 20–30 percent of the world’s seaborne oil passes — combined with the ongoing disruption of the Suez Canal route, has displaced the bulk of global oil transport onto what the IMO itself — in Resolution A.1192(33) — formally defines as the “dark fleet” or “shadow fleet”: aging, poorly maintained tankers operating outside international safety frameworks (including some operations to circumvent sanctions), evade safety and environmental regulations, and avoid insurance obligations.

“The geopolitical story here is about oil prices and military strategy,” said Mark J. Spalding, President of The Ocean Foundation. “The environmental story is about what happens when the world’s most dangerous cargo moves through its most sensitive waters on its least trustworthy ships — with no insurance, no oversight, and no one legally responsible for the cleanup. The world is not running out of oil. It is running out of safe ships to carry it.“

A Crisis Within a Crisis

Two of the world’s most critical shipping routes for oil and hazardous cargo remain severely disrupted during the current conflicts. The Strait of Hormuz, through which roughly 20% of the world’s daily oil supply ordinarily moves, and the Suez Canal have seen major carriers suspend operations entirely, and the situation continues to evolve rapidly.

The vessels still transiting the Strait — those operating under flags not subject to the current closure — are precisely the tankers that the international maritime community has spent years warning about. They average more than 16 years in age. Many lack a valid double-hull certification under MARPOL. Most operate without standard Protection & Indemnity (P&I) insurance from International Group clubs, meaning that if one runs aground or founders in the Persian Gulf, the Arabian Sea, or on the Cape of Good Hope, rerouting — now the only alternative for much of the world’s oil — coastal states bear the cleanup costs with no recovery mechanism. Before the conflict, the shadow fleet already accounted for almost a quarter of global crude oil exports, according to data provider Kpler. Since the closure, the majority of the remaining Gulf oil shipments have moved on vessels and cargo streams operating outside standard Western regulatory frameworks. The accountability gap has not merely persisted; it has become the primary mechanism by which the world is currently receiving its energy supply.

The shadow fleet did not emerge in a vacuum. Its dramatic expansion over the past decade is directly linked to the proliferation of sanctions regimes that have pushed significant volumes of global oil outside regulated shipping channels. That displacement created demand for vessels willing to operate outside international insurance, safety certification, and flag-state oversight. The environmental accountability gap the world now faces is, in part, a consequence of that policy architecture.

What We Know About the Environmental Risk

The Ocean Foundation has documented the shadow fleet’s environmental record in detail. Since 2021, satellite monitoring has confirmed at least nine oil spills from shadow fleet vessels. The fleet has not paused during the current conflict — satellite imagery captured at least eight simultaneous ship-to-ship oil transfers within a 10-kilometre radius near the Riau Archipelago just two days after the conflict began, confirming that the shadow fleet’s clandestine logistics infrastructure has accelerated, not stood down. In December 2024, two aging Russian tankers — the Volgoneft-212 and Volgoneft-239 — foundered in the Kerch Strait, releasing approximately 4,300 tonnes of heavy fuel oil into the Black Sea, contaminating over 60 kilometers of coastline and causing estimated ecosystem damage of €14 billion. Those vessels were 52 and 55 years old, operating well beyond their certified limits, engaged in ship-to-ship transfers that feed the shadow fleet supply chain.

The Hormuz crisis has multiplied this risk across three ocean basins simultaneously. The Persian Gulf is a semi-enclosed sea with exceptional biodiversity and limited water exchange — an oil spill in Gulf waters is not comparable to a spill in the open ocean. The Cape of Good Hope rerouting sends traffic through the South Atlantic and the Indian Ocean, where spill-response capacity is among the world’s most limited. The Caribbean, already identified by The Ocean Foundation as a region of acute shadow-fleet risk and inadequate infrastructure, faces additional pressure from the Panama Canal’s rerouting.

The Accountability Gap Is Now Structural

When a shadow fleet vessel causes an oil spill, there is typically no functioning insurance mechanism, no solvent responsible party, and no pre-positioned response capacity. Coastal states are left to choose between funding an expensive cleanup themselves or watching oil reach their shores. This was always a foreseeable consequence of the shadow fleet’s growth. It is now the baseline risk condition for a significant share of global oil transport.

The AIS monitoring environment has further deteriorated. U.S. maritime authorities have advised vessels in the region to turn off their AIS transponders for safety — creating a background of legitimate AIS silence that makes it impossible to distinguish from the systematic AIS manipulation that shadow fleet vessels routinely use to evade detection. Analysis of shadow fleet vessel behavior found that these ships go dark a quarter of the time overall, with vessels with sanctioned cargo switching off transponders in approximately 40 per cent of cases — a baseline of deliberate invisibility that the current conflict environment renders effectively undetectable. In the world’s most critical oil shipping lane, maritime authorities are now effectively blind.

What The Ocean Foundation Is Calling For

The Ocean Foundation today submitted a formal letter to IMO Secretary-General Arsenio Dominguez requesting an extraordinary MEPC session to address:

• Emergency Port State Control protocols for high-risk vessels displaced from normal trading routes, with mandatory insurance verification and hull certification checks
• Interim guidance on IOPC Fund activation and environmental liability for incidents involving uninsured vessels in the current crisis period
• A MARPOL Annex I enforcement circular reminding member states of their existing authority to enforce double-hull requirements and ship-to-ship transfer notification obligations
• AIS integrity standards that distinguish legitimate safety-based disablement from shadow fleet evasion tactics
• A dedicated assessment of response capacity gaps in the Persian Gulf, Indian Ocean, and Caribbean regions is now facing acute elevated exposure

“The IMO Council did exactly the right thing by convening an Extraordinary Session on March 18th and 19th — 120 Member States showed up, and the Secretary-General’s leadership was commendable,” Spalding said. “But the Council’s mandate is seafarer safety and freedom of navigation. The environmental accountability question — who carries the world’s oil now, under what conditions, and who pays when these vessels fail — belongs to the MEPC. The Council itself invited its committees to act within their mandates. We are asking the MEPC to do exactly that. The simultaneous closure of Hormuz and Suez is not a temporary disruption. It is a structural shift in who carries the world’s oil, and the environmental consequences will be borne by coastlines and communities with no voice in the geopolitical decisions that created this situation.”

Background: The Ocean Sentinel Response Initiative

The Ocean Foundation’s Ocean Sentinel Response initiative has been monitoring and documenting the environmental risks posed by the shadow fleet since 2024. Working with partners including the John Nurminen Foundation, Lloyd’s Register Foundation, and SkyTruth, the initiative has developed risk assessment frameworks, built partnerships with Baltic, Caribbean, and Indo-Pacific coastal states, and engaged with maritime policy bodies on proactive intervention strategies. The Foundation has applied for NGO observer status at the IMO. The current crisis represents the fulfillment of the environmental warnings the initiative has been raising — and an urgent test of whether international institutions can respond before a disaster forces reactive action.