Brent crude prices were trading at $100 a barrel on Wednesday for the first time since July, as escalating attacks across the Middle East fuelled concerns over disruptions to oil supplies from the region.
US struck Iranian tankers near the vital crude-export hub of Kharg Island, stoking fears of deeper disruptions in the Strait of Hormuz.
Brent crude prices have jumped by a quarter since early August as hopes for a permanent resolution to the six-month-old war faded and as fighting flared again. The global crude benchmark is up more than 60% this year.
The Middle East war intensified on Tuesday with Iranian-backed Houthis in Yemen launching strikes on several Saudi cities, further embroiling a U.S. ally in the conflict.
In a sharp escalation of the six-month-old war, U.S. forces hit multiple Iranian oil tankers and Iran targeted a U.S. base in Jordan and attacked ships.