The United Arab Emirates (UAE) is quitting the Opec and Opec+ groups of major oil producing nations next month after nearly 60 years of membership.
The UAE said its decision would help it meet growing global energy demand in the long term after recent investments to boost its production capacity.
It is seen as a blow to the cartel, which oversees oil production and has a major influence on the global prices - with one analyst describing the exit as "the beginning of the end of Opec".
The Gulf state's energy minister said being a country with no obligation under the group would give it more flexibility.
The UAE's departure represents a win for US President Donald Trump, who has previously attacked Opec for "ripping off the rest of the world".
In January, prior to the break-out of the US-Israel war with Iran, Trump asked Saudi Arabia and other Opec nations to "bring down the cost of oil" and doubled-down on his threat to use tariffs.
The move opens the door for closer ties between the UAE and US.
Saul Kavonic, head of energy research at MST Financial, said it was "the beginning of the end" for the alliance.
"With the UAE leaving, Opec loses about 15% of its capacity and one of its most compliant members."
Neil Atkinson, the International Energy Agency's (IEA) former head of the oil industry and markets division, said it is "a major blow to the future effectiveness" of Opec.
He told the BBC's Today programme that once normal oil production resumes after the war, Opec's ability to influence the direction of prices will be "clearly weakened".
The UAE "will attempt to sell as much oil as they can to as many people as possible", he said. "And that will run up against any attempts that the Opec group is making to keep prices high."
Atkinson said the war "has upended everything".
Last month, the IEA oversaw the release of 400 million barrels of oil in an attempt to curb the economic impact of the conflict.
However, oil prices remain elevated and on Tuesday they rose to $113 a barrel, compared to around $73 before the war began.
Opec was formed in 1960 by five countries - Iran, Iraq, Kuwait, Saudi Arabia and Venezuela - to defend the interests of major oil exporters by coordinating production to ensure steady revenue for its members.
The number of countries in the cartel has fluctuated over the years. In addition to the five founding members it also includes Algeria, Equatorial Guinea, Gabon, Libya, Nigeria and the Republic of the Congo.
The UAE joined in 1967, and its departure will leave the cartel with 11 members. There are an additional 10 non-Opec members in the wider Opec+ alliance, including Russia.
The UAE's decision came as the World Bank warned the war in the Middle East has caused the biggest loss of oil supply on record.
Energy prices will rise by about a quarter on average as a result this year, it said, while it could take six months for shipping through the key Strait of Hormuz to return to pre-war levels.
"The poorest people, who spend the highest share of their income on food and fuels, will be hit the hardest," said the World Bank's chief economist Indermit Gill.
The UAE's decision to leave Opec will not have an immediate impact on global energy supply, due to the ongoing closure of the Strait of Hormuz, but could lead to a longer-term boost in output.
The country has invested heavily in boosting its production capacity and has wanted for a long time to pump more oil, economists said.
David Oxley, chief climate and commodities economist at Capital Economics, said its departure could lead to lower oil prices but higher volatility on the market in the coming decades.
He added that while the UAE is small, the implications could be major if other member states leave, or countries such as Russia and Saudi Arabia decide to ramp up production as a result.
According to the latest figures from Opec, the UAE produced 2.9 million barrels of oil a day in 2024. Saudi Arabia, Opec's de facto leader, produced nine million barrels per day.
Experts suggested the UAE could boost oil production by around one million barrels per day outside of Opec.
Professor David Elmes of Warwick Business School said the UAE has one of the lowest "break-even prices" for oil it extracts, nearly half that of Saudi Arabia, meaning it can still turn a profit on oil it sells even when prices are lower.
"So the UAE wants to sell more and is less concerned with keeping prices high. Now they can do that," he said.
"Saudi Arabia will struggle to keep the rest of Opec together, and effectively have to do most of the heavy lifting regarding internal compliance and market management on its own," Kavonic said, adding other Opec members could follow suit.
"This presents a fundamental geopolitical reshaping of the Middle East and oil markets," he added.
