As Iran-US rhetoric heats up, the Strait of Hormuz chokepoint is again attracting concern that regional oil exports could be shut off. Saudi Arabia and the UAE both have pipelines bypassing Hormuz with capacity totaling 8.25mn b/d. But useable export capacity on these routes is considerably less. And Riyadh’s ‘Plan B’ relies on the Bab al-Mandeb strait where Yemen’s Houthis this week attacked Aramco tankers.

The latest bout of belligerent US-Iran rhetoric has once...