Very large crude carriers are now crossing the Strait of Hormuz and the Bab el-Mandeb in a "dark" mode for extended periods to move oil out of the Middle East. This tactic is an escalation of strategies developed in the early days of the Iran conflict. In the weeks following the outbreak of hostilities in late February, vessels carrying non-Iranian crude began disabling their transponders to avoid detection. At that time, these ships typically only turned off their transponders for a few hours while transiting the Strait of Hormuz.

Today, such covert voyages can last a week or more, with tankers reappearing thousands of kilometers away. This makes it difficult for ship-tracking agencies to determine what happened in between, a challenge compounded by the rise of "short-haul transshipment trade." In this model, crude oil is transferred to other vessels outside the Strait of Hormuz. A recent case in point is the very large crude carrier "Romania Prosperity." The ship vanished off the coast of Fujairah in the Gulf of Oman in late July, only to reappear nearby ten days later. Observers could not determine if it was still carrying its original cargo or had transferred it to another vessel and returned to the Persian Gulf for a new load. Ship-tracking data shows the "Romania Prosperity" has been operating near Fujairah and Sohar recently, but its long-term transponder shutdown makes it difficult to confirm its actual movements.

Another very large crude carrier, the "Alexandros," disappeared from the northern Red Sea in mid-July while empty and reappeared near India last week, partially loaded. Meanwhile, the very large crude carrier "Kuwait Prosperity" vanished in the Persian Gulf after loading crude in early July and turned up near Indonesia ten days later. Vessels shut off their transponders primarily to hide their location and avoid attack from Iran. With transport profits so lucrative, ship owners are willing to risk these dangerous chokepoints. In recent weeks, the Abu Dhabi National Oil Company has even begun shipping Iraqi crude through the Strait of Hormuz.

Maria Bertzeletou, Senior Market Analyst at Signal Ocean, says these "dark voyages" and other shifts in the freight market "indicate that the very large crude carrier market has adapted to a different operating environment. Confirmed tanker transits are becoming increasingly covert." According to Signal Ocean data, from July 14, when the US resumed its naval blockade of Iran, to early August, about 62% of crude oil and product tankers transiting the Strait of Hormuz were in "dark" mode, compared to roughly half before. The Signal Ocean data does not show the duration of the transponder shutdowns for these vessels.