LONDON — To understand just how contentious next week’s OPEC meeting will be, take a look at the confusion it’s created among professionals paid to predict the outcome.

The 20 analysts surveyed this week by Bloomberg are perfectly divided, with half forecasting the Organization of Petroleum Exporting Countries will cut supply Thursday in Vienna to stem a plunge in prices while the other half expect no change. In the seven years since the surveys began, it’s the first time participants were evenly split. The only episode that created a similar debate was the OPEC meeting in late 2007, when crude was soaring to a record.

The split now reflects the difficult choice OPEC nations have to make. They could cut output to revive crude prices from a four-year low, at the risk of losing more market share to rival suppliers, including U.S. shale drillers. Or they could do nothing and allow prices to fall low enough to deter growth in U.S. output, a move that would also squeeze the finances of poorer members like Venezuela and Nigeria. With half the analysts in the market headed for a surprise, prices will be volatile after the meeting, according to BNP Paribas.

“It’s going to be a critical day,” Doug King, chief investment officer of the $200 million Merchant Commodity Fund, said by phone from London on Nov. 14. “If there’s no action from the meeting, one of the most important OPEC meetings in the last 10 to 15 years, then the market will test them on the downside. If they cut 1.5 million barrels a day, you could get the Brent market back up into the $80 to $90 range.”

Oil collapsed into a bear market last month as U.S. drillers pumped at the fastest pace in more than three decades and global demand growth slowed. OPEC, responsible for about 40 percent of global oil output, needs to reduce production by 1 million to 1.5 million barrels a day to better balance supply and demand, Harry Tchilinguirian, head of commodity markets strategy at BNP Paribas, said by email from London on Nov. 11.

The group faced the opposite situation when analysts were at odds about OPEC’s intentions seven years ago. Brent futures had climbed about 55 percent in the 11 months up to the December 2007 meeting, putting pressure on the group to increase its production target. At the same time, the U.S. economy was on the verge of its worst recession since the 1930s, following a collapse in the housing market.

Before the meeting Dec. 5, 2007, 23 of 42 people surveyed by Bloomberg predicted OPEC would maintain its production target, while the others forecast an increase of between 500,000 and 750,000 barrels a day. On the day that the group decided to maintain output, Brent crude futures slumped as much as 1.9 percent, before settling 1.2 percent higher.

“If OPEC does nothing, I think we’re seeing this market get really trashed, another $10 from where it is,” Hakan Kocayusufpasaoglu, chief investment officer at Archbridge Capital, a Zug, Switzerland-based hedge fund, said by phone Nov. 14.

The group’s decision is made more difficult by the size of the supply cut needed to offset growth in production outside OPEC, Kocayusufpasaoglu said. “They’re going to have to cut 2 million barrels a day over time,” he said. “That’s a lot of money to leave on the table.”

U.S. crude production will surge 800,000 barrels a day to a 43-year high of 9.4 million in 2015, adding to 1.1 million barrels a day of growth projected for this year, the Energy Information Administration said Nov. 12.

Back in 2007, production of oil from shale rock formations that’s driving the current boom had barely started. North Dakota’s Bakken formation, one of the biggest shale oil producers in the U.S., pumped just 33,000 barrels a day in December 2007, barely 3 percent of the 1.12 million barrels a day it produced in September, data from the North Dakota Industrial Commission shows.

There’s only a “remote possibility” OPEC will agree to a cut in Vienna, Seth Kleinman, Citigroup’s head of European energy research, said in a report Nov. 10. Members including Algeria, Nigeria and Venezuela are unwilling to reduce their own production while Saudi Arabia, the group’s biggest producer, will refuse to do so alone, he said.