Hormuz dark-ship flows reach 710,000 bpd as strait stays restricted

Gulf oil reserves bottlenecked behind the strait have fallen from a peak of 184 million barrels on 22 March to approximately 148 million barrels this week, according to Kpler data. That implies an average withdrawal rate of around 500,000 barrels per day (bpd) across the conflict period, accelerating to roughly 710,000 bpd since the start of May. The direction of travel is positive, but context matters: before hostilities, the strait carried an estimated 13 million bpd of crude and products, and shipping monitors LSEG and Kpler both record only an average of three tankers transiting per day since the conflict began, approximately one-tenth of normal volumes.

The mechanism behind the uptick is the deliberate suppression of vessel tracking. Ships are reportedly disabling their AIS both before and after the crossing, a tactic previously used by Iran to circumvent Western sanctions. In practice, tankers can disappear from satellite monitoring for days around the strait and reappear weeks later near discharge ports in Asia. Vortexa estimates that 65% of laden tankers left the Gulf in so-called dark mode during May. Some vessels are understood to be operating under limited passage agreements Iran has negotiated with Pakistan, India, China, and Japan; others may be routing close to Oman's coastline with implicit support from the U.S. Navy. The specific breakdown remains opaque by definition.

What this means for UK buyers and forward curves

Brent over the past six months provides the benchmark against which any sustained Hormuz reopening, or fresh disruption, would be priced.

For UK commercial energy buyers, the Hormuz situation feeds directly into the global crude benchmark that shapes UK gas import economics and, through carbon and gas linkages, into power prices. A genuine, sustained reopening would add meaningful downward pressure to Brent and, by extension, to National Balancing Point (NBP) front-month contracts. The current partial recovery, driven by dark-ship activity rather than a negotiated settlement, introduces a different kind of risk: flows that could be interrupted at short notice if talks between the U.S. and Iran stall or collapse.

Key variables to track across the coming weeks:

• Kpler Gulf floating-storage levels (currently c.148 million barrels, down from 184 million barrels peak)
• Daily tanker transit count through Hormuz (currently averaging three per day versus c.30 pre-conflict)
• AIS dark-mode prevalence as a share of laden departures (65% in May, per Vortexa)
• Insurance war-risk premiums on Gulf voyages, which continue to deter fleet redeployment
• Progress, or absence of it, in U.S.–Iran negotiations toward a formal reopening
• Return flows of empty tankers, the logistical precondition for restarting the c.11 million bpd of suspended production

The empty-tanker problem is underappreciated. Onshore storage in the Gulf is near capacity, and suspended oilfields, estimated at roughly 11 million bpd of shut-in production, will not restart without confidence that laden outflows can be matched by a reliable return of ballast vessels. Shipowners and charterers remain cautious; insurance pricing reflects that caution.

Even a political breakthrough may not restore the strait to its pre-war configuration. Tehran has signalled an intention to retain traffic-control authority and introduce a tolling mechanism, which would structurally alter one of the world's critical oil chokepoints. Gulf producers facing that prospect may accelerate investment in alternative export routes, but those solutions take years to build at scale. Watch the U.S.–Iran negotiating timeline and the next set of Kpler floating-storage readings; if the drawdown rate stalls or reverses, expect Brent and NBP forwards to respond quickly.