The Iran war — and the accompanying oil and gas crisis it set off — remains far from resolved. On Saturday, a marathon day of negotiations between Iran and the U.S. in Pakistan ended with no agreement in place. Vice-President J.D. Vance said Iran “chose not to accept our terms,” which he framed as reasonable; Iran countered that “excessive demands” by America prevented any agreement. One of those demands was for Iran to immediately reopen the Strait of Hormuz, the crucial waterway that it has largely closed to commercial traffic since the U.S. and Israel began bombing Iran in late February. Unsurprisingly given the leverage it has gained from closing the strait, Iran refused to do so without a comprehensive peace plan in place. Then on Sunday, President Trump announced via Truth Social that the U.S. would begin a complete blockade of the strait beginning Monday morning, in a probably quixotic attempt to pressure Iran into buckling.

None of this promises to ease the dire consequences of the strait’s closure, including soaring oil and gas prices and shortages of jet fuel, fertilizer, and other goods that are battering economies around the world, especially in Asia. But how much worse might things get under a blockade? And what does a best-case scenario look like now? For answers to these questions, I turned to Gregory Brew, a senior analyst on Iran and oil at the Eurasia Group who writes extensively on both topics, including in the book Petroleum and Progress in Iran.

Is this blockade an effective or sustainable strategy for the U.S.? What are the chances it actually gets Iran to concede anything?The U.S. has the forces ready to impose a blockade on Iran, but it would require constant effort — Iran conducts tens of billions of dollars in seaborne trade, carried on hundreds of ships every year — and it would need to be sustained over a period of time to be effective at squeezing Iran economically. Even then, I’m not sure it would force Iran to make concessions beyond what it is already considering. Iran has been under sanction for decades, its leadership is hardened to such pressure, and while the blockade would surely affect ordinary Iranians, the regime possesses the repressive power needed to quell domestic unrest.

Given that the strait was barely open before this anyway, how much worse would a blockade make the overall economic fallout from this conflict?In the short term, this brings the volume of traffic through the strait down to zero, since ships will either face the threat of Iranian attack if they don’t pay the toll or the risk of U.S. seizure if they do. The Iranians are almost certain to respond with aggressive moves against regional shipping if their own ships are waylaid or their ports blockaded. So the trickle of ships getting through the strait at the moment will dry up, compounding the economic effects by worsening the supply impact. To take just one example: Right now, Iran is exporting 2 million barrels per day in........

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