Not a fully shut strait — just a filtered one: Washington said its navalblockade of Iranian ports is fully operational, with over a dozen warships and aircraft enforcing it. Within the first 24 hours, some merchant vessels were ordered to turn back — yet at the same time, some vessels continued to transit Hormuz.

Ins and outs

Who, then, was still getting through? “Early signals indicate that limited transits are still occurring under defined conditions, particularly where voyages are clearly non-Iranian in destination or where cargoes fall within humanitarian or essential goods classifications,” Daejin Lee, global head of research at Fertmax, tells EnterpriseAM.

Vessel-tracking data showed that some ships continued to transit Hormuz — including sanctioned tankers. The Murlikishan — a tanker under US sanctions and linked to networks that have moved Iranian oil — likely passed because it was bound for Iraq to load fuel oil rather than calling at an Iranian port. Panama-flagged Peace Gulf — a regular carrier of Iranian naphtha via Hamriyah — was also allowed through.

Who was turned back? Around six merchant vessels were ordered to reverse course in the first 24 hours, which indicates enforcement is real, but selective. The Rich Starry — another sanctioned tanker — had to turn back after initially transiting the strait. It had loaded roughly 250k barrels of methanol in Hamriyah, placing its voyage somewhere between a breakthrough and a false start.

Our take

The pattern points to a narrower reality: the blockade does not treat Hormuz as fully shut. Restrictions appear focused on ships heading to or from Iranian ports and nearby coastal areas, rather than all traffic through the strait — which explains why some vessels were still able to pass even as Washington said the blockade was fully in force.

What’s the next phase of pressure?

Storage is the next pressure point: Iran continued exporting crude during the conflict, but the strategy now is to choke those outbound flows long enough to force a production response once storage begins to fill.

How quickly does the squeeze bite? Not immediately. Iran appears to have roughly 10-15 days before storage constraints start pushing it toward output cuts. Tanks are still only a little over half-full, with additional barrels potentially parked offshore.

The window is narrowing — with Washington closing the temporary 30-day waiver of sanctions that had let some Iranian oil already at sea keep moving. The waiver has allowed roughly 140 mn barrels of oil to reach global markets. However, Iran still has a land border and alternative import routes, limiting how much a naval squeeze alone can isolate the country.

What to watch

The question is whether the blockade will erode the structural advantage Iranian-linked vessels have held since 28 February — and whether it will undermine the viability of bilateral-arrangement tonnage and the informal IRGC toll system that has underpinned transit access throughout this crisis…. the first real signs should come from vessel traffic over the next few days,” Lee adds.

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