US crude oil is now trading around $53 a barrel, down from a four-year high above $76 in early October. Brent crude has plunged to $62 from above $86.
Led by Saudi Arabia, OPEC will also seek Russian backing for supply restraint to put a floor underneath prices. The alliance between OPEC and the world's second largest producer dates back to 2016, when they first agreed to cut production to halt a damaging collapse.
The International Energy Agency warned last month that supply is expected to exceed demand through 2019. In its November market report, OPEC said demand for its oil next year would be about 1.1 million barrels a day less than in 2018, and 1.4 million below current OPEC production.
But Saudi Arabia's approach to this week's meeting has been complicated by intense public pressure from President Donald Trump on the kingdom to allow prices to fall even further.
"Hopefully OPEC will be keeping oil flows as is, not restricted," Trump tweeted on Wednesday. "The world does not want to see, or need, higher oil prices!"
Here are three possible outcomes from the Vienna meeting:
Analysts say this is the most likely outcome, despite the pressure from President Trump.
Eurasia Group said in a report published last week that it expects an agreement by OPEC and Russia to cut a combined 1.5 million barrels a day from the market.
"While discussions will not be easy, Saudi Arabia will succeed in rallying the OPEC and non-OPEC group to decrease output," it said.
The kingdom said last month it would cut 500,000 barrels a day from its production in December. It pumped 10.6 million barrels of oil in October, before going even higher in November.
"A ramp-up of Saudi production to 11.2 million barrels per day is probably a tool used by Riyadh to press for a deal in Vienna, as a sign of its ability to bolster production compared to the other OPEC countries that are more constrained," said Eurasia Group.
But some analysts say Saudi Arabia may seek a modest cut to try to balance the demand from Trump for lower prices with the interests of OPEC members.
However, a cut of one million barrels a day or less may not be enough to stabilize a market that is awash with oil.
That would leave the market "fairly disappointed," said Warren Patterson, commodities strategist at ING. "It likely [won't] be enough to balance the market over the first half of 2019."
Analysts believe this is the least likely outcome. For the past few weeks, OPEC members have been rallying support to trim supply.
Russian officials had signaled that it was too early for a cut. But there are signs Moscow may now be on board.
Most OPEC members would like higher prices to balance their budgets. In Saudi Arabia, oil accounts for about 70% of government revenue and the energy sector makes up 40% of the economy.
An agreement to maintain production at current levels is "highly unlikely given the high break evens most governments need, especially in the Gulf," said Mohamed Bardastani, senior economist for the Middle East at Oxford Economics.