The price of crude oil jumped 5% today, shortly after US President Joe Biden left open the possibility of Israel striking Iran’s oil industry in response to Tehran’s missile attack.

Biden, asked if he would support an Israeli strike on Iran’s oil facilities, the US president replied: “We are discussing that.”

Iran is the world’s seventh largest oil producer, exporting about half of its production abroad, mainly to China. After Iran’s missile attack on Israel, crude oil prices rose 10% to $77 a barrel for Brent crude.

Even now, however, it remains below the price levels it hit earlier this year, as weaker demand from China and ample supply from Saudi Arabia work to keep prices down.

But the escalation of violence in the Middle East, and the threat of further escalation, is weighing on oil markets. Of particular concern is the possibility of an escalation that could lead to the closure of the Straits of Hormuz, through which a third of oil tankers and a fifth of liquefied natural gas LNG pass.