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.

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."