New Delhi, Aug. 27 -- Tighter US economic sanctions designed to squash Iran's economy ought to have worsened global energy-supply anxiety. Yet, the oil market has shown signs of relief in recent days.

Notwithstanding US President Donald Trump having claimed the Strait of Hormuz as US territory, crude oil prices slumped below the $90 per barrel mark after Iran and Oman said they had discussed joint operation of a shipping path through the contested strait. Brent crude oil dropped about 6% in two days to $85 per barrel on Wednesday.

The market's response reveals who it sees in control of that vital sea passage: Iran or the US. America's blockade of Iranian trade is in place, of course, but China's rejection of US efforts to isolate Iran h...