Oil is priced by the barrel. But where are all the barrels? In "The business of a barrel," we look at why the barrel remains a global standard for measuring, pricing and trading oil — even though crude oil is no longer transported in actual barrels!

However, whether this "barrel" standard can sustain now hinges on the fate of a narrow waterway. The continued navigability of the Strait of Hormuz is a factor that's now inextricably linked to how much real meaning the global energy market's "standard unit" still carries.

US President Donald Trump said on Saturday that he has rejected a conditional proposal by Iran concerning the reopening of the Strait of Hormuz.

"They want to make a deal, and I think that's fine. I like making a deal too, but that deal would not be acceptable," he added.