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When Iran set up their blockade in the Strait of Hormuz, what exactly was it intended to block? Which countries were being denied access? For example was it intended to block both import and export between US allies, but all other trade was allowed? Did Iran's blockade hurt their own economy, and if so, why did they do it?

How is the US's imposed blockade different than Iran's? Is it so that Iran can no longer export and do business with its allies (which presumably was still happening when it was just the first blockade)?

It seems like most countries' economies are being damaged by the blockades and none are benefiting from it. What are the objectives, to pressure the other side into agreeing to demands?

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  • most countries' economies are being damaged yes, however the impact is less in North America which can affect global perception. Also the impact will significantly worsen when the Russia oil at sea is depleted. Russia oil depots in the west are out of service. Commented 10 hours ago

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TLDR

  • The US blocks ships that are coming from Iranian ports

  • Iran blocks ships that aren't from a select list of friendly countries (we can debate whether they are "blocking" or "not blocking", but the numbers speak for themselves - few ships transited, even before the US blockade).

  • With some exceptions, like China and India-linked ships, either Iran will want to block a ship or the US will want to block it.

What the US is doing and why

Well, the weird thing about the start of this war was that Iran got increased revenue from its oil:

Once Iran, entirely predictably, started to block Hormuz to "unfriendly countries' ships" (a fuzzy notion that excludes or has excluded at times Russia, China, Pakistan, India and some others, which are "friendly") oil prices started to go up.

Trump at that point wanted to tamper the oil price back down so announced a relaxation of first, Russian oil sanctions and second, and bizarrely Iranian oil sanctions.

Then we get the ceasefire, but Iran puts in place the "toll booth" whereby tankers have to transit Hormuz through Iranian territorial waters and, at least in some cases, pay a $1-2M fee to be let through.

The situation immediately after the start of the cease-fire.

Iran-friendly ships are let through, Iranian oil benefits from a premium and most non-Iran oil is still stuck in the Gulf. This is another unwelcome development. It's a blockade, by Iran, but selective so that it can still make money.

The "solution"?

Add another blockade, American this time, further out, not in Hormuz proper, at the entrance to the Gulf of Oman. Ships "affiliated with Iran" or at least coming from Iranian ports are impeded, by the Americans, not the Iranians. So, in theory, no more Iranian profits.

The problem left over

  • Ships will not be seized by the US Navy if transiting in Pakistani or Indian territorial waters.

  • The US will also find it difficult to risk going after Chinese or Indian-flagged ships.

    • but they have been pretty good at intercepting "dark fleet", falsely flagged tankers.

  • Generally speaking, on the US side of things, ships have been either

    • left alone (there are widely differing accounts of how many are making it through)
    • told to turn back
    • herded off to holding areas (more the dark fleet ships than others)
    • fired up on rare occasions.

  • The overall oil supply is even more constrained than previously.

What's going on with Shipping? on April 26th, 2026 offers the qualified opinion that the US's doubled-up blockade is probably working to pressure Iran. While the channel is run by an American who covers shipping matters in depth, he is quite critical of Trump's war planning, so his assessment that it might be working and is not the stupidest idea embarked on so far by Trump in this war shouldn't be dismissed out of hand, I think.

SkyNews YouTube - April 28th, 2026 also claims that Iran may be facing a big problem in 2-3 weeks: running out of storage to put their oil into. Problem being that a wellhead can be damaged, permanently or longterm, if oil flow can't be maintained out (oddly enough, the Gulf States seem at less risk from what others have been saying: "merely" months to get them going again).

What Iran is doing.

Look at any wargame, strategic analysis, movie plot, etc... of the last 40 years and many of them will tell you the same thing: Iran will turn off the world's oil spigot by shutting down the straits of Hormuz. In the 2000s, there was even a bit of a kerfuffle when a US Navy exercise simulating a wargame shutting this type of channel down by an unnamed (but very Iran-like) adversary got gamed: the red team general outsmarted the US by fighting differently and... sunk a bunch of simulated US ships.

(sorry, the wargame was so prescient that I'll quote some of it)

... CJTF-South seized these islands and established a controversial military escort service to protect ships navigating through the region, charging a toll for its services. This led to a direct military response from "Blue," whose primary objectives were to secure international shipping lanes, neutralize Red's weapons of mass effect (WME) capabilities, and restore sovereignty over the disputed islands...

So, when the US attacked Iran on Feb 28, 2026, Iran did exactly what had been predicted. Except that, unlike the 2000s we now have drones and cheap missiles allowing swarming and saturation attacks. Look at the travails of the Russian Black Sea Fleet: this would be a very hard nut to crack.

So Iran can, and did, effectively shut down the strait to anyone it didn't want to transit. That's pretty much everyone except the friendly ones mentioned above. That doesn't hurt the US directly, but it hurts everyone else and it does hurt American consumers when oil prices go up and they need to fill up their SUVs.

And since ships carrying its own oil were, for a while, the only ones allowed through, Iran profited to boot.

p.s. Iran has talked of mines. Whether those have actually been emplaced is unclear. Iran has mines, but any mined area is a problem for everyone, including friendly forces. For now, none of their attacks have seemed to involve mines and no actual mine sightings have taken place. They might use them later, but for now they seem to privilege weapons over which they have more direct control than mines.

p.p.s. There are usually about 140 transits per day in the strait and right now it seems to be running at 5-10 on good days. US military ships have largely stayed out of it except for a few occasions: mines can be a real problem and the area is too narrow for a combat ship to maneuver effectively in.

p.p.p.s.

The effects are pretty big. About 10% of oil supply is shut off. Some portion of Gulf States' oil can be pipelined to the Red Sea (but might be bottled in if the Houthis seriously get involved and blockade the straits off Yemen). LNG supplies Europe relies on are held up. Different countries rely more or less heavily on Gulf-origin oil and some are really hurting, like Sri Lanka. And a big underreported problem is that fertilizers, which often use oil as feedstock, are also effectively blockaded, giving the possibility of crop failures later on.

Here's an image from "What's going on with shipping" that I annotated:

enter image description here

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    Well, the US uses its control over the international financial system (via the US Dollar's place in it) to impose its own sanctions on others: companies in many countries have been told not to buy Iranian oil, lest they get access to the international banking system shut off: it's not about the US not trading with Iran, it's about the US prohibiting others to trade with Iran. aljazeera.com/news/2026/4/25/… Commented 2 days ago
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    @ESamual Already asked . About the US, but answer is roughly similar for Canada - our gas pump prices have also gone up. Commented 2 days ago
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    @ESamual Gas prices are always global. Plus, not oil is the same; the US may be a net exporter, but it imports some as well. Commented 2 days ago
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    @ESamual One important reason is that, if prices are higher elsewhere, US and Canadian companies make more money exporting oil instead of selling locally, so if a local refinery/gas station wants access they need to pay more too. This can prevented through export control laws, but so far the US doesn't seem to be interested in that, probably because it'll really piss off the oil companies currently making a lot of money. Commented yesterday
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    @ESamual Oil is a global commodity. It doesn't matter much for the oil prices the US pays if, say, Iranian oil is blocked specifically and the US doesn't buy from Iran. Someone else who was buying from Iran still needs oil, and they become a competitor for other sources of oil that the US does buy. This is all still true even if the US is a net exporter of oil: companies that export US oil will do well, but everyone in the US that consumes global oil (anyone who uses gasoline or diesel, for example, not to mention plastics manufacturing and other industries) sees higher prices. Commented yesterday
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Iran did not set up a blockade in the Strait. It set up a toll booth, with a "friendly warning" that the Southern passage through the strait, which is in international waters, might have mines. The Northern passage comes through Iranian territorial waters and they're requiring payment.

The US did set up a blockade against Iran. Per international law, blockade is a form of war consisting of stopping or disabling all ships coming to or from the blockaded nation's ports. It specifically excludes preference to ships of select nations, so a declaration of blockade implies intention and ability to completely cease shipment through the blockaded ports, regardless of who it's from and who it's for.

In practical terms:

  • Israeli and aligned ships may be attacked if they attempt to transit the strait (legal for belligerents, but Iran is using a loose definition of "aligned")
  • Neutral ships are being requested a toll by Iran (generally illegal).
  • Trump has claimed he'll sink neutral ships which pay such a toll (war crime, should be refused as illegal orders).
  • As well as ships coming to/from Iran (legal under the laws of war).
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    Why exactly would it be illegal for Iran to attack Israeli and aligned ships transiting the strait, but legal for the US to attack ships coming to/from Iran? Israel is hardly a neutral country. Commented yesterday
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    @user111403 Attacking Israeli and US ships is completely legal. But Iran is extending the threat to ships which have merely done trade with Israel in the past. Commented yesterday
  • Clear enough, thanks for the edit. In practice though it seems like this means one can only impose a blockade at the point of destination, rather than the point of departure. Which, cynically, one might say is rather convenient for a handful of powerful countries. Commented yesterday
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    @user111403 That was largely the intent: to make only top naval powers able to declare blockades. Iran is basically rewriting the law more than interpreting it. Commented yesterday

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