Roughly one-quarter of the non-Iranian large oil tankers trapped inside the Persian Gulf at the outbreak of the Iran war have managed to slip out in a slow, stealthy trickle.

Twenty-nine of the 109 bigger vessels, those capable of hauling 700,000 barrels or more, which were stranded when the Strait of Hormuz was effectively shuttered after the conflict erupted on February 28 have now crossed the chokepoint, shipping data compiled by Bloomberg show. 

While that flow is a fraction of the crude and oil products still locked inside the Gulf, the cargoes have been snapped up by a global market in which inventory buffers are shrinking at a record pace. And with many ships switching off instruments that broadcast their positions, the real number may well be higher. 

Faced with the sporadic hostilities of the three-month conflict, the ships have had to resort to unconventional maneuvers to make the passage. Some have made the crossing under the cover of darkness as they strive to avoid the threat of rockets launched from shore. In some cases, the governments of countries taking the cargoes have been forced to lobby for the privilege.

Iran-linked ships have been excluded from the calculation, as these had free passage through Hormuz until mid-April. Most did not broadcast position signals in the Gulf even before the latest conflict erupted, complicating the tracking of Iranian flows.

Oil traders have been fixated on ships’ attempts to pass through the strait since its closure triggered the biggest energy-supply disruption in history and sent prices for vital fuels soaring. Control over the corridor is central to tortuous negotiations between the U.S. and Iran aimed at ending the conflict.

Chevron Corp. Chief Executive Officer Mike Wirth said on May 29 that the company currently has six vessels in the Gulf that are under charter. It will be the ship owner who decides whether or not to move through the strait, Wirth said. TotalEnergies SE CEO Patrick Pouyanne said that — once it can extract the eight tankers it has stuck in the Gulf — the company will wait to see “if peace is sustainable” before sending any back. 

With ships having to proceed so cautiously, the flow of oil they’ve transported has been modest, equating to about 520,000 barrels a day — a fraction of crude and products still shuttered inside the Gulf. It’s also eclipsed by flows through the alternative pipelines being used by Saudi Arabia and the United Arab Emirates to divert exports away from the strait.

But in addition to providing badly needed supplies to a global market nervously watching the break-neck depletion of inventories, the successful transits also free up a portion of the global fleet that can return to the Gulf and collect cargoes once a peace agreement is struck. 

“In the very near term, with inventory draws and demand erosion, the fact that so many have made it out is contributing to the downside on price,” said Naveen Das, senior crude oil analyst at analytics firm Kpler Ltd. “However, if this status quo continues and inventories globally continue drawing to low levels, the amount of vessels stuck starts becoming more alarming and could be viewed as a real problem again.” 

Most vessels made the transit by “going dark” — switching off the Automatic Identification System used to communicate their position — with many having done so at the start of the war. Widespread interference with these signals has only clouded the picture further.

As a result, the tally of ships that made it out could be under-reported. Of those tankers yet to escape, almost 20% haven’t transmitted signals on their locations so far this month. 

Alternative Routes

Hormuz was declared closed by Tehran in the immediate aftermath of joint U.S.-Israeli strikes on the country at the end of February. While Iran was initially able to continue oil exports, Washington retaliated with its own blockade on the Islamic Republic’s shipments in mid-April.

The crossings are only a fraction of the typical Hormuz transits before the war, which accounted for about a fifth of the world’s oil supply. 

Iran has sought to establish a virtual “toll booth” for ships crossing the strait, demanding fees of as much as $2 million for a single transit along its shore at the northern side of the waterway, between the country’s Larak and Qeshm islands. It’s not clear how successful Tehran has been in making shipowners pay up.   

Other Gulf nations like Saudi Arabia and the United Arab Emirates considered the procedures presented by their regional rival — which has attacked their territories during their conflict — as untenable. An alternative route was possible to the south, close to Oman. Some vessels attempted a journey through the strait, only to later abort it.

The category of ships most closely watched is composed of so-called very large crude carriers — which can haul 2 million barrels of oil — and Suezmaxes, which can transport about half that volume, as well as slightly smaller Aframaxes.

Whether traffic picks up will depend on the diplomatic process. The U.S. and Iran have reached a preliminary deal to extend a ceasefire by 60 days and discuss the future of Tehran’s nuclear program, a person with knowledge of the matter said, buoying hopes for a resolution to a conflict that has killed thousands and roiled the global economy.