The price of Brent crude, the international benchmark, gained 3.9% to $78.96 per barrel, while the US benchmark crude oil price rose 4% to $74.26 per barrel.
Prices for both types of crude oil had recently slipped back to the levels seen before the war with Iran began, after the two sides reached an interim agreement to end the conflict and ships resumed transporting oil through the Strait of Hormuz.
However, the United States launched several waves of strikes on Iran early on Monday morning following an Iranian attack on a container ship in the Strait of Hormuz that set the vessel ablaze and left one crew member missing over the weekend. Iran retaliated by targeting countries across the Middle East.
US stock futures fell, with the contract for the S&P 500 down 0.4% and that for the Dow Jones Industrial Average 0.3% lower. Nasdaq Composite futures lost 1%.
In Asian trading, Tokyo's Nikkei 225 index lost 1.1% to 67,786.86, while in Seoul, the Kospi declined 5.6% to 7,060.69.
