Oil tankers used to sail down the middle of the Strait of Hormuz.
But since Feb 28, any seeking to cross the 21-mile-wide waterway have had to take a detour.
In what has become known as the “Tehran Tollbooth”, vessels must now head closer to the Iranian coastline, nosing themselves between the islands of Qeshm and Larak.
Ship owners then go through a complex – and expensive – process of negotiation.
First, according to Bloomberg, they are required to inform intermediary companies linked to the Islamic Revolutionary Guards Corps (IRGC) of the ship’s cargo, destination and ultimate owner.
Iran then charges a “toll” of at least $1 per barrel, with the rate rising according to the perceived friendliness of the national operator.
Fees must be paid in Chinese yuan, or a cryptocurrency. The average rate for a single oil tanker is $2m (£1.5m). If everything is approved, IRGC boats will finally provide an escort into and out of the “tollbooth”.
Some analysts believe it could make as much as $500bn (£377bn) in five years.
This system – informal and illegal for now – represents Iran’s biggest win from the war with the United States. It is now the target of the two-week ceasefire announced by Donald Trump. The US President has stated that the pause in fighting is strictly “subject to” the “COMPLETE, IMMEDIATE, and SAFE OPENING” of the Strait of Hormuz.
However, Iran’s statement said that any crossing had to be carried out “in conjunction” with the Iranian military – something very different to free passage – and an Iranian official told AP that the deal allowed Tehran to still charge fees.
The next two weeks will see which system holds.
Left in place, it could earn a vengeful rogue state hundreds of billions of dollars and fundamentally reshape both the Middle East and maritime trade around the world.
That prospect makes its long-term survival unlikely, analysts told The Telegraph.
“Iran has learned how to keep the global economy in a hostage situation,” said Petras Katinas, a research fellow at the London-based Royal United Services Institute think tank.