The global oil supply could possibly fall by 40% overnight.
Iran has threatened to block the Strait of Hormuz in response to US sanctions.
The Strait of Hormuz is the narrowest part of the Persian Gulf. Oil from producing countries like Saudi Arabia Qatar and the United Arab Emirates also ship their oil through the strait. All up 40% of the oil produced around the world each day goes through this narrow channel.
The Strait of Hormuz is a weak point in global oil shipping