Nymex processed several incorrect oil and gas prices Friday, leading trading platforms to show spikes that never happened.

Trading is now functioning properly, but the incorrect prices may still show up on screens run by other data providers and used by traders and brokers, a CME Group Inc. spokesman said. One of those other companies, CQG, was still trying to correct its prices late Friday morning, a spokesman said.

CQG, a commonly use trading platform, showed front-month natural gas spiking 50% in one minute just before 10:30 a.m. EST, and then later showed a dip of 24%. Peter Donovan, broker for Liquidity Energy in New York, said he uses a different platform that showed a 32% spike in December 2018 crude futures to $88.10, a spike so large he dismissed it out of hand.

"You lose confidence in the accuracy of the system," he said about the incident. "Nobody wants to have any exposure if there's a technical issue."

Several traders and brokers reported seeing similar numbers, but said they had no problem trading. They dismissed the numbers as anomalies.

Nymex workers inadvertently processed the data and have since removed all of it, according to CME's statement. "Trading in our Nymex energy markets continues to function properly and is referencing current intraday market prices," it said.

Write to Timothy Puko at tim.puko@wsj.com

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