Oil prices plunged more nearly 5 percent on Thursday after OPEC and other major exporters extended their current deal to limit oil production for nine months, disappointing investors who were anticipating deeper cuts.
OPEC and other major producers, including Russia, will roll over their six-month deal to remove 1.8 million barrels a day from the market through March 2018. Investors had hoped the cartel might reduce output even further to drain a global glut that has depressed the market for almost three years.
Brent crude oil plunged $2.52, or 4.7 percent, to $51.44 a barrel by 2:36 p.m. ET (1836 GMT). U.S. West Texas Intermediate (WTI) crude futures ended Thursday's session down $2.46, or 4.8 percent, at $48.90.
The S&P 500 energy sector was trading down nearly 1.8 percent for its worst day since May 4.
Crude oil futures fell sharply lower around midday, after paring losses throughout the morning.
Michael Cohen, head of energy markets research at Barclays, said the market may have been looking for "the icing on the cake," such as deeper output cuts or limits on exports.
"When those things weren't included, then this kind of movement happens. We remain constructive on oil prices for next couple months as inventories draw down," he told CNBC in an email.
Khalid Al-Falih, Saudi Arabia's energy and industry minister, said he was not concerned by daily market moves during a press conference following OPEC's meeting.
Ahead of closed-door meetings, Falih told CNBC, "Nine months with the same level of production that our member countries have been producing at is a very safe and almost certain option to do the trick."
Saudi Arabia's delegate said all options had been considered ahead of the announcement, including deeper cuts and a possible six-month extension.
OPEC also discussed extending the cuts through June 2018 if the market deteriorates, sources told Dow Jones. That option would be decided near the end of the nine-month extension and could be triggered by high global stockpile levels and low oil prices, the sources said.
Miswin Mahesh, an oil analyst at Energy Aspects, told CNBC via telephone that "oil prices are always choppy" when OPEC meetings are in session.
He added that the price fall on Thursday morning "was probably triggered" by "imbalances" in the market with some expecting deeper cuts to OPEC production.
OPEC is trying to drive crude stockpiles in developed nations down to the five-year average. They currently stand about 300 million barrels above that level.
Surging U.S. production, spurred by higher oil prices, combined with weak fuel demand and persistently robust OPEC exports in the first half of the year to offset the cartel's production cuts. That has left global stockpiles near record highs.
Deeper cuts would likely put
"Compounded by seasonal demand growth, the cuts should help accelerate global inventory drawdowns over the balance of the year and will likely set a new floor for crude oil prices in the low $50 per barrel range," he said in a statement.
Still, energy consultancy Wood Mackenzie said keeping existing oil output at current levels for another nine months would result in a 950,000 barrels per day production increase in the United States, thus undermining OPEC's efforts to balance supply and demand.
U.S. oil production has already risen by more than 10 percent since mid-2016 to more than 9.3 million
Investors are also nervous about rising output from Nigeria and Libya, which are exempt from cutting production as they attempt to restore supplies sidelined by internal conflicts. Falih said OPEC members Nigeria and Libya would still be excluded from cuts.
— Reuters contributed to this story.