Brent crude, the international standard, spiked to nearly $120 on Monday before falling back but was still at around $90 a barrel on Tuesday, nearly 24% higher than when the war started on Feb. 28. The Dow Jones Industrial Average drifted lower at the open Tuesday.

Iran has effectively stopped tankers from using the Strait of Hormuz, through which 20% of the world’s oil is carried. Attacks on merchant ships near the strait have killed at least seven sailors, according to the International Maritime Organization.