The move to release oil stocks came as Iran said it was ready for a long war of attrition that would "destroy" the world economy, after firing on two commercial ships and threatening any vessels from the United States or its allies.
The IEA announced that its member countries would unlock 400 million barrels of oil from their reserves to mitigate the impact of supply disruptions through the Strait of Hormuz.
Tehran has retaliated against US and Israeli attacks that began on February 28 by attacking targets across the oil-rich Gulf and effectively shutting down the crucial Strait of Hormuz, through which nearly 20 per cent of the world's oil usually transits to world markets.
Despite the IEA announcement, oil prices jumped more than four per cent.
While it may be a record reserves release, it still replaces only part of the lost supplies, noted analyst Helge Andre Martinsen at DNB Carnegie.
He estimated that releases from strategic reserves could total 1.75 million barrels per day, while lost supply is approximately 11 million barrels per day of crude and around four million barrels per day of oil products.
"Hence, it will help, but it won't make a massive difference for the very short-term global oil balance," he said.
Robert Yawger from Mizuho USA pointed to lingering questions about the timing of the release, adding that Tuesday's quickly deleted Trump administration post, erroneously reporting a successful Strait of Hormuz tanker escort, had raised questions.
"The 400 million barrel number (is obviously) very large, and it implies that the problem is very large," Yawger said.
Equity markets were not reassured either. Wall Street indices finished mostly lower while European markets closed in the red.
"With the IEA's record oil reserves release unable to push prices lower today, this is keeping risk appetite downbeat, with stock markets struggling and currencies of oil-importing regions lower," said Forex.com analyst Fawad Razaqzada.
Oil volatility
Fears that the conflict could drag on -- choking off energy supplies -- sent both main crude contracts soaring on Monday to within a whisker of $120 a barrel, the highest since 2022. Natural gas prices also rocketed.
Prices dropped on Tuesday after US President Donald Trump said the war was "going to be ended soon", before turning higher again.
"Markets are likely to grow increasingly fearful over the long-term implications with each day that passes," said Joshua Mahony, chief market analyst at Scope Markets.
New attacks hit three commercial ships in the Gulf on Wednesday, officials said, leaving one vessel in flames as Iran pressed its campaign against its oil-exporting neighbours.
US group Citi also dampened sentiment, consultancies Deloitte and PwC and other firms in Dubai, which closed offices or asked employees to evacuate on Wednesday after Iran threatened US and Israel-linked economic assets in the Middle East.
The evacuations at the heart of the Middle East's financial hub come as the Gulf, but especially the UAE, has borne the brunt of Iran's attacks in response to US-Israeli strikes.
Key figures at around 2115 GMT
Brent North Sea Crude: UP 4.8 per cent at $91.98 per barrel
West Texas Intermediate: UP 4.6 per cent at $87.25 per barrel
New York - Dow: DOWN 0.6 per cent at 47,417.27 (close)
New York - S&P 500: DOWN 0.1 per cent at 6,775.80 (close)
New York - Nasdaq Composite: UP 0.1 per cent at 22,716.13 (close)
London - FTSE 100: DOWN 0.6 per cent at 10,353.77 (close)
Paris - CAC 40: DOWN 0.2 per cent at 8,041.81 (close)
Frankfurt - DAX: DOWN 1.4 per cent at 23,640.03 (close)
Tokyo - Nikkei 225: UP 1.4 per cent at 55,025.37 (close)
Hong Kong - Hang Seng Index: DOWN 0.2 per cent at 25,898.76 (close)
Shanghai - Composite: UP 0.3 per cent at 4,133.43 (close)
Euro/dollar: DOWN at $1.1574 from $1.1611 on Tuesday
Pound/dollar: UP at $1.3419 from $1.3418
Dollar/yen: UP at 158.92 yen from 158.05 yen
Euro/pound: DOWN at 86.25 pence from 86.52 pence
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