Other oil-producing countries are too small or hamstrung by political constraints to control the conversation. Over the last two years, the Saudis, the world’s largest exporters, and Russia, which has been producing about 12 percent of world output, have called the shots.

A high-five between President Vladimir V. Putin of Russia and Crown Prince Mohammed bin Salman at the Group of 20 summit meeting in Argentina last week was a sign of how closely their interests are aligned.

“We call it OPEC, but it is a whole different system now,” said Bhushan Bahree, an OPEC analyst at IHS Markit, a research firm. “The managing committee is just two countries.”

Last summer, for instance, Saudi Arabia and Russia opened up the taps — in response to complaints about rising prices from the United States and other producers — leading to price declines and now-present worries about oversupply. The move brought complaints from other members, notably Iran, that the Saudis run OPEC for their own benefit.

What is likely to happen?

Most analysts say that the oil producers have little choice but to announce a substantial cut in production of at least one million barrels a day, or around 1 percent of world oil supplies. Otherwise, prices could slide into the $40-a-barrel range or lower, squeezing the oil-dependent economies of member countries.

The purpose of cuts is to reduce supplies, to bolster prices and to change market psychology.

“They need to cut because otherwise there will be a massive oversupply next year,” said Ann-Louise Hittle, an analyst at Wood Mackenzie, a market research firm.

What does Qatar’s announcement that it will leave OPEC mean?

Qatar, like Iran, appears to be fed up with Saudi Arabia’s dominance of OPEC. The minister of state for energy affairs, Saad Sherida al-Kaabi, explained the decision on Monday by saying that the oil business was “controlled by an organization managed by a country,” apparently referring to the Saudis. Qatar will leave next year.