The heads of missions of the member states, OPEC Secretary General Haitham Al Ghais, and representatives of the media have participated in the meeting in the Austrian capital.

OPEC and its allies are debating a new deal possibly adjusting countries' output quotas and a further cut in production, sources told Reuters, as the group faces flagging oil prices and a looming supply glut.

OPEC+, which groups the Organization of the Petroleum Exporting Countries and allies led by Russia, pumps about 40 per cent of the world's crude, meaning its policy decisions can have a major impact on oil prices.

Four sources familiar with OPEC+ discussions have told Reuters that additional production cuts were being discussed among options for Sunday's session.

"We are discussing the full package (of changes to the deal)," one of the four sources said.

Three out of four sources said cuts could amount to 1 million bpd on top of existing cuts of 2 million bpd and voluntary cuts of 1.6 million bpd, announced in a surprise move in April and which took effect in May.

The April announcement helped to drive oil prices about US$9 per barrel higher to above US$87, but they swiftly retreated under pressure from concerns about global economic growth and demand. On Friday, international benchmark Brent settled at US$76.

If approved, the new cut would take the total volume of reductions to 4.66 million bpd, or about 4.5 per cent of global demand.

Typically, production cuts take effect the month after they are agreed but ministers could also agree on a later implementation. They could also decide to hold output steady.

OPEC+ ministers will start gathering from 11am local time on Sunday in Vienna and have a full meeting from 12am onwards, according to sources familiar with the latest schedule.

Last week, Saudi Arabia's Energy Minister Prince Abdulaziz said investors who were shorting the oil price, or betting on a price fall, should "watch out", which many market watchers interpreted as a warning of additional supply cuts.

Three OPEC+ sources also said that the group will address the issue of baselines for 2023 and 2024, from which each member performs cuts.

Such talks have previously turned contentious.

West African countries such as Nigeria and Angola have long been unable to produce in line with their targets but have opposed lower baselines because new targets could force them to perform real cuts.

By contrast, the UAE has insisted on getting higher baselines in line with its growing production capacity, but that would mean its share in the overall cuts might decrease.

Western nations have accused OPEC of manipulating oil prices and undermining the global economy through high energy costs. The West has also accused OPEC of siding too much with Russia despite Western sanctions on Moscow over the war in Ukraine.

In response, OPEC insiders and watchers have said the West's money-printing over the last decade has driven inflation and forced oil-producing nations to act to maintain the value of their main export.

Asian countries such as China and India have bought the lion's share of Russian oil exports and refused to join Western sanctions on Russia.