The price of Brent crude, the benchmark for Europe, rose by almost 19 per cent to nearly $US111 ($A159) per barrel (159 litres) in early trading on Monday.
Earlier, at the start of trading in Chicago, the West Texas Intermediate (WTI) grade, which is the benchmark in the US, had jumped above the $US100 ($A143) mark - a price level last seen in 2022.
On Friday afternoon, Brent crude oil for delivery in May was trading at over $US90 ($A129) for the first time since April 2024.
Before the start of the Iran war just over a week ago, the price was still around $US70 ($A100) per barrel. Fuel prices have also risen significantly since then.
Fears of a prolonged blockade of the Strait of Hormuz remain a dominant concern for the oil market. Since the US-Israeli attacks on Iran, hardly any ships have passed through the strait in the Gulf.
In peacetime, around a fifth of the world's oil trade is transported through this strait. It is also very important for the transport of liquefied gas, for example from Qatar.
US President Donald Trump, for whom rising fuel prices could become a problem in view of the important midterm elections later this year, tried to shift the focus to the long-term development.
"Short term oil prices, which will drop rapidly when the destruction of the Iran nuclear threat is over, is a very small price to pay for U.S.A., and World, Safety and Peace," Trump said in a post on his Truth Social platform, adding in all caps: "Only fools would think differently!"
At the end of last week, Qatari Energy Minister Saad al-Kaabi warned in an interview with the Financial Times of the serious consequences of the war in the Middle East for energy supplies from the region.
Al-Kaabi said there were fears that all oil-producing countries in the Gulf could halt production within a few weeks. According to the minister's assessment, this could lead to an increase in the price of oil to as much as $US150 ($A215).
Due to the de facto blockade of the Strait of Hormuz, some producers are running out of storage capacity.
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