The price of oil sank more than 9% on Monday on hopes that a pause in attacks between US and Iran could help lead to a resolution to the conflict.
Brent crude, the global benchmark for oil, dipped below $88 a barrel, marking a sharp turnaround from last week when it had risen above $100.
The fall came after the US ambassador to the UN said attacks on Iran had been halted for a second night in a row to give "talks some space" .
An Iranian army spokesperson said on Sunday that Tehran had halted "retaliatory" attacks in the region in response.
The outbreak of the Iran war triggered a sharp rise in oil prices as the conflict led to the effective closure of the Strait of Hormuz, a key shipping route which usually carries about 20% of the world's oil and liquefied natural gas (LNG).
When Iran and the US signed a memorandum of understanding in June to halt military operations and reopen the strait, the price of oil fell back to pre-war levels of around $70 a barrel.
However, the collapse of the ceasefire earlier this month reignited fears over global energy supplies and pushed the oil price back up.
Last week it hit $100 a barrel for the first time since May, with added concerns coming after Houthi militia in Yemen attacked oil tankers in the Red Sea, threatening a key export route that Saudi Arabia had used to bypass the Strait of Hormuz.
Susannah Streeter, chief investment strategist at Wealth Club, said markets were remaining "cautious given the twists and turns during this conflict".
Despite the sharp fall in crude, "there is still significant uncertainty baked into these prices and a reticence about whether negotiations will lead to a lasting breakthrough," she added.
The conflict between the US and Iran - and its impact on oil - has pushed up the cost of fuel such as petrol and diesel in many countries.
This often has knock-on effects on other prices, such as food, as businesses pass on the higher costs they are facing to customers, and this can push up the rate of inflation.
