Iran war: Tankers use stealth to exit Strait of Hormuz, freeing trapped oil

The trickle of tankers exiting the Strait of Hormuz has gathered pace in recent weeks, as traders adopt stealth measures to make the crossing. While this is freeing some of the vast oil inventories trapped in the Gulf, it does not signal a slow return to normalcy. Instead, it previews the opaque, fragmented energy market the Iran war is set to leave in its wake.

More than four months into the conflict, the U.S. and Iran are still struggling to hammer out an agreement to formally end the war and fully reopen the narrow waterway.

The near-total closure of Hormuz stranded more than 13 million barrels of oil per day within the Gulf, forcing producers to shut down oilfields and refineries, triggering supply shortfalls and economic strain across major importing nations.

Traffic through the strait remains a fraction of pre-war levels. On the face of it, an average of just three tankers a day has crossed in and out of Hormuz since the conflict began - roughly one-tenth of normal volumes - according to shipping monitors including LSEG and Kpler.

But a closer look at oil stocks tells a more nuanced story.

An analysis of the huge volumes stored on tankers inside the Gulf suggests transit activity has quietly accelerated. It points to a growing number of ships leaving the region "under the radar" of satellite tracking systems.

More vessels appear to be switching off their Automatic Identification System (AIS) before and after transiting the strait, adopting tactics long used by Iran to evade Western sanctions.

In practice, tankers can "go dark" for days around the crossing, only to reappear weeks later near their destination.

Shipping analytics firm Vortexa estimates that around 65% of outbound laden tankers transited in “dark” mode in May, showing how widespread the practice has become.

That opacity is distorting the market's line of sight. Reduced visibility into cargo movements and destinations makes it harder to gauge the flows underpinning benchmark pricing.

That makes alternative indicators increasingly important.

One key gauge of the pace of outflows is “oil on water” in the Gulf, or the volume of oil stored on tankers trapped behind the strait.

Levels have dropped from a peak of 184 million barrels on March 22 to around 148 million barrels this week, according to Kpler data, implying an average drawdown rate of roughly 500,000 bpd.

Crucially, that pace has accelerated over the past month. Since the start of May, depletion has increased to around 710,000 bpd, according to ROI analysis. That offers further evidence that flows out of the Gulf, while still constrained, are inching higher.

Exactly which routes these dark tankers are taking remains unclear – as the term “dark” suggests. Many are likely using corridors designated by Iran, which has allowed limited volumes through the strait under bilateral arrangements with Asian governments including Pakistan, India, China and Japan. This underscores the region’s heavy dependence on Gulf supply. Some vessels may be paying Iran a fee for safe passage.

Other vessels may be taking routes closer to Oman’s coastline, potentially with the tacit or active support of the U.S. Navy, which continues to play a stabilising role in regional maritime security.

The situation remains fluid and could shift quickly. Iran could tighten its grip on shipping at any moment, particularly if negotiations with the U.S. continue to stall.

After more than three months of severe economic disruption, every barrel exported offers a lifeline to revenue-starved Gulf producers such as Iraq and Kuwait, and desperate buyers in Asia.

But a sustained recovery will require far greater clarity and stability around Hormuz. Producers are unlikely to restart the roughly 11 million bpd of oilfields shut in during the conflict without confidence that exports can flow reliably. One key constraint is logistical: the return of empty tankers to the Gulf. Without a steady inflow of vessels to load cargoes, onshore storage tanks will remain near capacity, preventing the restart of shut-in production.

That crucial rebalancing - laden ships leaving and empty ships returning - has yet to materialise at scale.

Shipowners and charterers remain wary of sending vessels into a region where the risk of becoming stranded remains high. Insurance premiums continue to reflect that elevated risk, reinforcing a cautious approach to redeploying fleets.

Ultimately, the market may never return to normal, even if a political breakthrough officially “reopens” the strait.

Tehran is seeking to retain control over traffic in the waterway and introduce a tolling system, potentially reshaping how one of the world’s most critical oil chokepoints operates. That would represent an untenable situation for Gulf producers, forcing them to find alternate routes. And if they can’t erode Iran’s position strategically, they may seek to do so militarily.

The shift toward a more opaque trading environment in the Middle East may be providing some marginal relief. But the fragmented, dangerous reality it reflects means any respite may be short-lived.