Oil prices fell on Friday to their lowest levels in more than a year, deepening a rapid seven-week sell-off that has plunged crude futures deep into a bear market.

Friday's declines further ramp up the pressure on OPEC ahead of a much-anticipated meeting between the influential oil cartel and its allies in Vienna on Dec. 6, when they are expected to announce that output will be curtailed.

So far, the prospect of the Middle East-dominated group orchestrating a fresh round of supply cuts has done little to prop up crude futures.

U.S. benchmark West Texas Intermediate crude ended Friday's session down $4.21, or 7.7 percent, at $50.42. WTI hit its weakest price since mid-October 2017 on Friday.

International benchmark Brent crude dropped $3.66, or 5.9 percent, to $58.94 by 1:34 p.m. ET. The contract hit its lowest level since late October 2017.

WTI has now lost 34 percent of its value from its peak on Oct. 3 to the trough on Friday. Brent has fallen as much as 32 percent.

"I have to say that the speed in which the oil market has declined has surprised me even as OPEC and non-OPEC members discuss a production cut," said Andrew Lipow, president of Lipow Oil Associates. "The market does not think it will be enough."

The latest wave of energy market selling comes amid escalating concerns about an increase in global supply and a slowdown in economic growth.

Saudi Energy Minister Khalid al Falih on Thursday said the kingdom's output this month would surpass October's production of 10.6 million barrels per day.

That is near an all-time high but below the 10.7 million bpd guidance for October that Falih announced last month. Falih also said in October that November output would hit 11 million bpd. Sources told Bloomberg News this week the Saudis are currently pumping a record 10.8 million to 10.9 million bpd.

Falih on Thursday said demand will be lower in January and the kingdom will respond to weaker consumption. The minister has already warned Saudi oil shipments will fall by 500,000 bpd in December.