Executive Assessment

Developments over 1–2 September have reinforced that the strategic contest over the Strait of Hormuz is changing. For decades, analysis of Iranian maritime leverage focused primarily on whether Tehran could close the Strait through mines, missiles, fast attack craft or direct attacks on merchant shipping. Those capabilities remain relevant, but the current operating environment suggests Iran is attempting something broader.

The Persian Gulf Strait Authority has established a non-compliant vessel regime that threatens listed ships with fines, detention or confiscation and extends potential exposure to vessels involved in ship-to-ship transfers or transshipment with designated ships.¹

At the same time, the military environment around Hormuz remains active. The United States and Iran carried out their largest exchange of attacks since July on 1–2 September, with US strikes against Iranian military infrastructure followed by Iranian missile and drone attacks against US-linked bases across the region.²

Recent tanker attacks, unresolved Iranian claims concerning sea mines, reduced commercial transit and the continued relevance of IRGC small craft mean the PGSA regime is not being introduced into a normal commercial environment. It is being introduced into a battlespace.

That gives Iranian regulatory threats greater coercive weight.

From Maritime Disruption to Maritime Governance

Iran has long possessed tools capable of making navigation through Hormuz dangerous. Mines, anti-ship missiles, drones, fast attack craft, boarding teams and vessel seizures have all formed part of the threat environment.

What is changing is the relationship between those tools and commercial regulation.

The PGSA has told cargo owners to consult its non-compliant vessel list before fixing ships for voyages involving the Arabian/Persian Gulf. It has also said vessels interacting commercially with designated ships can themselves be added to the restricted list.³

This introduces a new proposition into voyage planning. A vessel may no longer be assessed solely on its flag, ownership, sanctions status, class, technical condition and war-risk exposure. Its previous interaction with PGSA-designated vessels may also matter.

Iran is therefore attempting to influence not simply whether ships can move through the Strait, but the commercial history and relationships attached to those ships.

Secondary Exposure Is the Critical Mechanism

The most important element of the PGSA regime is not the original blacklist itself. It is the potential for exposure to spread.

Iran has warned that vessels engaged in ship-to-ship transfers or transshipment with blacklisted ships can also face designation.³

This resembles the behavioural logic of secondary sanctions, although the PGSA regime does not possess equivalent legal standing or international recognition.

The comparison is nevertheless useful because both mechanisms rely heavily on anticipated consequences.

A commercial actor does not need to be penalised before changing behaviour. It only needs to conclude that the risk of future enforcement outweighs the value of the transaction.

Commercial Behaviour Is Already Responding

There is evidence that the PGSA regime is already influencing commercial decisions.

Reuters reported that at least three Indian refiners and a major international energy company had decided to avoid vessels on Iran’s blacklist, including in ship-to-ship operations.⁴

That is strategically more important than the number of vessels physically detained.

If companies decline to charter listed vessels because they anticipate future interference, then the PGSA is already producing a compliance effect without requiring universal enforcement.

This is the point at which maritime coercion begins shifting from direct action towards behavioural control.

STS Workarounds Create a Strategic Vulnerability

Ship-to-ship transfers have become more important because commercial operators are trying to preserve Gulf energy flows while reducing exposure to Hormuz.

Reuters reported on 2 September that three LNG cargoes from Qatar and the UAE had recently been transferred between vessels outside the Strait for onward delivery to India and Japan. LNG STS transfers are normally unusual, highlighting the degree to which the market is adapting to disruption.⁵

Several vessels involved in those operations appear on the original PGSA blacklist, including GasLog Shanghai, Al Rekayyat and Mraweh.⁵

This creates an important contradiction.

The same commercial mechanism being used to reduce exposure to disruption — ship-to-ship transfer outside Hormuz — is also the mechanism Iran says can transmit non-compliant status to another vessel.

The PGSA regime therefore potentially extends Iranian leverage beyond the Strait itself.

Physical Threat Gives the Regime Credibility

A vessel blacklist issued during stable conditions could be largely ignored.

The same blacklist carries different weight when merchant vessels are being attacked, the mine threat remains unresolved and US and Iranian forces are actively exchanging strikes.

Reuters reported that Iran’s IRGC claimed two tankers had been disabled by sea mines, although the claim remains unverified and other reporting on recent tanker incidents describes unidentified projectiles.⁶

The distinction matters because a projectile attack is primarily an immediate event. A mine threat can create persistent uncertainty over where vessels can safely navigate even after active exchanges subside.

Small craft provide another layer. Iran’s ability to use fast vessels for surveillance, harassment, boarding and diversion means PGSA rules potentially have a physical enforcement mechanism available close to the shipping lanes.

The relevant strategic question is therefore not whether mines, missiles, drones or small craft constitute the principal Iranian maritime threat.

It is whether they collectively make Iranian instructions sufficiently credible to influence commercial behaviour.

The Battlespace Is Expanding Around the Strait

The renewed US-Iran military exchange reinforces the point that Hormuz can no longer be treated as an isolated shipping-security problem.

Reuters reported that US forces struck strategic Iranian military facilities along the southern coast before Iran retaliated against US-linked bases in Bahrain, Jordan, Kuwait and Iraq.²

The relevant operating environment now connects southern Iranian military infrastructure, Gulf air bases, energy terminals, commercial shipping lanes and maritime enforcement activity.

Closure Is No Longer the Right Measure of Iranian Leverage

The traditional question surrounding Hormuz has been whether Iran can close it.

That is increasingly the wrong threshold.

Commercial traffic can be materially impaired while the Strait remains technically open. Reuters reported only limited commodity-vessel movements during the latest escalation, while energy prices rose sharply as markets reassessed the risk to Gulf supply.⁶

Strategic leverage can instead be created through friction: delayed departures, reduced chartering appetite, additional insurance cost, route restrictions, STS avoidance, AIS suppression, convoy requirements, vessel vetting and uncertainty over future access.

None of those requires a formal closure.

Taken together, however, they can materially alter the economics and operating patterns of one of the world’s most important energy corridors.

Legal Authority and Operational Influence Are Different Questions

The PGSA’s asserted authority over Hormuz remains internationally contested.

The IMO Council has previously urged states to reject attempts to impose unilateral control over navigation through the Strait.⁷

This means the PGSA should not be presented as an internationally recognised maritime regulator.

But legal recognition is not the same as operational influence.

Commercial actors frequently adjust behaviour because of physical risk before disputes over jurisdiction are resolved.

A shipowner can reject Iran’s legal claim while still choosing to comply with its instructions because the vessel, crew and cargo remain exposed.

That distinction is central to understanding the PGSA regime.

What Has Changed

The distinction is fundamental.

Closing Hormuz imposes enormous economic costs on Iran and the wider region. Selectively influencing movement may provide a more sustainable form of leverage.

Tehran can potentially allow some cargoes to pass while increasing the cost, risk or uncertainty faced by others.

That is closer to controlled friction than outright blockade.

Strategic Implications

For shipowners and managers, PGSA designation could become another voyage-planning consideration alongside war risk, sanctions, technical status and charter requirements.

For charterers and cargo interests, secondary exposure creates the possibility that a vessel’s previous commercial relationships affect future access through Hormuz.

For insurers, PGSA designation introduces a potential distinction between general regional war risk and exposure created through the deliberate use of vessels Iran regards as non-compliant.

For Gulf energy exporters, STS transfers and alternative loading arrangements provide important resilience but may also create new exposure if Iran attempts to extend its compliance regime through vessel-to-vessel interaction.

For regional governments, the PGSA represents a challenge not only to freedom of navigation but to the conditions under which commercial access to Gulf ports and cargoes is determined.

For the United States, degrading Iranian military capability may reduce the physical threat without necessarily dismantling the commercial architecture Tehran is attempting to establish.

Indicators to Watch

01 — Further PGSA designations
Whether the blacklist continues expanding and whether particular ownership nationalities, vessel classes or cargoes become overrepresented.

02 — Secondary designation following STS
The first confirmed case of a vessel being blacklisted because of interaction with an already-listed ship.

03 — Physical enforcement
Boarding, detention, diversion or seizure explicitly justified through PGSA non-compliance.

04 — Route enforcement
Evidence that vessels are being compelled to use Iranian-approved transit arrangements.

05 — Mine geography
Independent evidence linking mine activity to routes Iran describes as unauthorised.

06 — IRGC small-craft activity
Increasing interaction with commercial vessels on compliance or routing grounds.

07 — Charterer avoidance
More refiners, energy companies or traders declining to use PGSA-listed vessels.

08 — Insurance response
Changes in cover, exclusions or pricing linked explicitly to PGSA designation.

09 — Delisting
Evidence that vessels can successfully obtain removal from the PGSA list and what conditions Iran requires.

10 — International countermeasures
Additional IMO, GCC, US or European action challenging Iranian enforcement.

P&C Assessment

Assessment Confidence

HIGH CONFIDENCE that Iran is seeking to influence commercial behaviour through mechanisms extending beyond direct attacks on shipping.

HIGH CONFIDENCE that the PGSA regime creates potential secondary exposure through ship-to-ship transfers and related commercial interaction.¹

MODERATE CONFIDENCE that the PGSA is developing into a longer-term coercive compliance architecture rather than remaining a temporary wartime measure.

MODERATE CONFIDENCE that Iran’s physical maritime capabilities increase the effectiveness of PGSA restrictions even where enforcement remains selective.

LOW TO MODERATE CONFIDENCE regarding the extent and current location of active Iranian mine deployment in or around commercial transit routes.

---

Sources

1. Reuters, “Iran threatens 45 tankers with fines, confiscation in Hormuz escalation,” 24 August 2026. Source

2. Reuters, “US pounds Iran, Tehran strikes back at bases in biggest exchange since July,” 2 September 2026. Source

3. Reuters via Khaleej Times, “Iran warns vessels violating Hormuz transit rules of fines, detention,” 24 August 2026. Source

4. Reuters, “Some oil companies to avoid ships on Iran blacklist, sources say,” 26 August 2026. Source

5. Reuters, “Qatari, UAE LNG cargoes transferred via ship-to-ship outside Strait of Hormuz,” 2 September 2026. Source

6. Reuters, “Oil retreats from one-month high as traders weigh supply risks,” 2 September 2026. Source

7. Reuters, “Countries must reject Iran efforts to control Hormuz, UN agency document says,” 10 July 2026. Source

8. Power & Corridors, “The PGSA Blacklist: Iran’s Expanding Maritime Compliance Regime in the Strait of Hormuz,” 2 September 2026. Reference Dataset

---

Power & Corridors Intelligence
Strategic Assessments examine the implications of developing events beyond the immediate incident cycle. Assessments reflect information available at the time of publication and may change as new operational, commercial and maritime evidence emerges.