Behind the standoff inside OPEC over whether to boost oil production is a key cartel member with a new strategy: sell as much crude as possible before demand dries up.

The United Arab Emirates’s strategy, as described by officials familiar with the matter, represents one of the most significant shifts in oil policy by a major Mideast petrostate. For years, the region’s oil-producing governments have said they aren’t worried about finding crude buyers far into the future. The U.A.E., which holds some of the world’s largest untapped crude reserves, is breaking from that orthodoxy, according to people familiar with the strategy.

“This is the time to maximize the value of the country’s hydrocarbon resources, while they have value,” said a person briefed on the U.A.E.’s strategy. “The aim of the investment is to generate revenue for the diversification of the economy, both for investment in new energy and, as importantly, in new revenue streams.”

The country isn’t worried about a sudden drop in demand, and expects to have buyers for its crude for decades. However, people familiar with the new tack say the country wants to pump and sell as much as it can now, when demand and prices are strong. Proceeds will help it wean its economy off oil.

“Market share is a key factor here,” said a senior U.A.E. oil executive. “We want a bigger market share, to monetize as much as we can from our reserves, especially when we have spent billions developing them.”

Spokespersons for the U.A.E.’s energy ministry and the Abu Dhabi government didn’t reply to requests for comment.

In recent days, the U.A.E. has been the lone holdout regarding a deal to boost crude output among members of the Organization of the Petroleum Exporting Countries and a group of Russia-led oil producers, together known as OPEC+. Last week, the rest of OPEC+ tentatively agreed on a deal to gradually unwind the deep cuts members enacted at the start of the pandemic. At the time, the group cut 9.7 million barrels a day of crude, amounting to about 10% of 2019 demand. The group has reinstated about 4 million barrels of that.

The U.A.E. has said it would agree to the plan to gradually release the rest only if it can boost its own output inside the group’s complex quota system. Saudi Arabia, OPEC’s de facto leader, has so far refused that concession, triggering a rare, public feud between the two allies. Neither side appeared to budge Wednesday, obscuring the outlook for oil prices.

For bulls, a no-deal means that OPEC+ keeps current production ceilings intact, even as economies reopen and demand grows. OPEC members say they are doing just that. Oil bears are betting a no-deal could lead members to abandon the system altogether and pump whatever they want.

After the group failed to resolve the deadlock earlier this week, U.S. crude hit six-year highs before retreating. Midday Wednesday in London, West Texas Crude was up 1.8%, around $74.70. Brent crude, the international benchmark, was up 1.6%, at above $75.60.

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The pandemic stalled factories and shut down business around the world, causing a historic drop in oil demand just as production was reaching new highs. (Originally published April 16, 2020) The Wall Street Journal Interactive Edition

The spat has drawn U.S. intervention, amid rising gasoline prices there. Over the weekend and into this week, high-level U.S. officials have had conversations with officials from Saudi Arabia, the U.A.E. and other relevant countries, said White House spokeswoman Jen Psaki.

Amid a recent geopolitical divergence, the U.A.E and Saudi Arabia are diverging over how to respond to what many analysts, officials and executives say is a global transition away from high carbon-emitting fossil fuels. “The historic alliance is being tested,” said Christyan Malek, who is in charge of global energy at JP Morgan & Chase. “The rivalry is no longer just in the oil market, but for the post-oil economy.”

In the short term, both countries have boosted oil production, promising to put the proceeds into investment that will help them diversify away from fossil fuels.

In 2020, Saudi Arabian Oil Co., known as Aramco, said it planned to increase its sustainable oil production capacity from 12 million to 13 million barrels a day. A few months later, the U.A.E.’s Abu Dhabi National Oil Co. announced it would be spending $122 billion in part to boost its oil production capacity to 5 million barrels a day by the end of the decade, from about 4 million today.

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The International Energy Agency, estimates that global oil demand will plateau in 2030, the year Abu Dhabi expects to hit its 5 million barrels a day goal.

The U.A.E.’s proven reserves—the oil it still has under the ground—is estimated at 98 billion barrels, according to the BP Statistical Review. At a 5-million-a-day rate, that would take more than 50 years to pump.

The U.A.E. is “in the race for market share ahead of peak demand,” said Robin Mills, chief executive of Dubai-based consulting firm Qamar Energy and a former manager in the Emirati oil industry. Unlike other OPEC members, Saudi Arabia and the U.A.E. have the opportunity to boost production capacity, he said.

Saudi Arabia has publicly said it isn’t worried about demand drying up and stranding its reserves. In June, Saudi Energy Minister Prince Abdulaziz bin Salman, at an OPEC+ press conference, was asked about a report by the IEA recommending halting investment in hydrocarbons to reach net-zero carbon emissions by 2050.

“I believe it is a sequel to the “La La Land” movie,” he said. “Why should I take it seriously?”

—Andrew Restuccia contributed to this article.

Write to Benoit Faucon at benoit.faucon@wsj.com, Summer Said at summer.said@wsj.com and Stephen Kalin at stephen.kalin@wsj.com