Oil costs surged by nearly 20 percent after 2 attacks on Saudi Arabian departments on Saturday knocked out more than 5% of the world’s stock.

The strike, which the US accuses on Iran, has sparked fears of heightened risk to energy supplies in the country.

The drone strikes on plants in the heartland of Saudi Arabia’s oil production hit the world’s biggest petroleum processing facility as well as a nearby oil field, both of which are produced by energy giant Aramco.

Together they account for about 50% of Saudi Arabia’s oil output or 5% of everyday global oil production. It could take weeks before the facilities are fully back online.

The Saudis have given little detail about the attacks, apart from saying there were no casualties, but have given a few more hints about oil production.

Energy Minister Prince Abdulaziz bin Salman announced some of the falls in production would be built up by tapping huge warehouse facilities.