OPEC and a Russia-led group of producers failed to agree on how to meet fast-rising demand from the industrialized world, as the club of rich nations emerges from pandemic lockdowns.

This week’s meeting of the Organization of the Petroleum Exporting Countries, and its Russia-led allies, dubbed OPEC+, has been hampered by conflicting signals about short-term and long-term demand. Some of the historical dynamics of the oil markets have been thrown upside down by the pandemic.

Demand growth from the developed world, which for years has stagnated, is on a tear as it emerges furiously from Covid-19 lockdowns. Meanwhile, the developing world—the source of almost all new oil demand in years past—is still sputtering.

A week ago, OPEC and allied producers led by Russia were leaning toward boosting production by half a million barrels a day, with more additions possible later in the year, The Wall Street Journal reported.

Going into formal deliberations being held virtually this week, Saudi Arabia, OPEC’s de facto leader, and Russia had agreed to take up a proposal that includes a boost of about half a million barrels a day starting in August, according to people familiar with the talks, and then gradually increasing OPEC+ output by a total two million barrels through December.

Those talks ended inconclusively, after the United Arab Emirates objected, according to delegates.

The group cut 9.7 million barrels a day of production at the start of the pandemic, and has so far restored about 4 million barrels a day of that.

On Friday, most delegates agreed to a deal that would call for OPEC+ to increase production by 400,000 barrels a day each month through late 2022, which would undo remaining curbs of about 5.8 million barrels a day.

The U.A.E. again balked, according to delegates.

Another wrinkle: A deal may be conditional on the status of Iran sanction talks with the world powers. Tehran is negotiating a resumption of an Obama-era deal in which it would curb its nuclear ambitions in exchange for a lifting of sanctions on oil sales.

Oil prices are now at their highest since late 2018. On Friday, Brent crude oil, the international benchmark, closed up 0.4% above $76 a barrel, and U.S. futures ended almost unchanged at $75.20 a barrel.

Accelerating vaccination drives in the U.S. and Europe are boosting global economic activity—and by extension, demand for oil. OPEC data showed markets needed two million barrels a day of extra oil this year. Meanwhile, the Delta variant of the coronavirus has wreaked havoc in India, an anchor of oil-demand growth in normal times.

China, too, is seeing signs of economic softening as consumers pull back amid isolated outbreaks there. The country is also struggling with supply bottlenecks that have hampered production.

For now, the thirst for oil from richer countries has become the key short-term demand driver. OPEC expects oil demand in industrialized nations to increase by 2.7 million barrels a day in 2021, up 6.3%. More than half of that growth will come from the U.S., at 1.5 million barrels a day, it said. The trend will accelerate in the second half, with a consumption boost of 3.1 million barrels a day.

Write to Summer Said at summer.said@wsj.com and Benoit Faucon at benoit.faucon@wsj.com