Oil prices plunged more than $5 in a few minutes on Monday afternoon as volumes spiked in a rapid sell-off, sending Brent crude crashing through technical support as markets sought an explanation for the plunge.

Brent crude oil [LCOCV1 113.13 -3.53 (-3.03%) ] sank from $115.20 a barrel at 1:52 p.m. to $111.60 three minutes later as trading volumes — which had been muted by the Rosh Hashanah holiday — shot up. Brent crude later pared losses to settle $2.87 lower at $113.79 a barrel.

Ten thousand lots traded in one minute during the drop, up from 152 lots the minute before prices plummeted. Brent crashed through the 200-day moving average before beginning to recover.

U.S. crude [CLCV1 96.00 -3.00 (-3.03%) ] also dropped, but not as deeply as Brent.

U.S. light, sweet crude fell $2.38 to settle at $96.62 a barrel. U.S. oil pared losses slightly after dropping sharply in a 20-minute span and at one point falling 4.4 percent a barrel. That's its biggest intraday swing since early June.

It was not immediately clear what caused the crash, but traders said it could have resulted from a problem with a computer trading program.

The market has also been watching for any move to release crude oil from the U.S. Strategic Petroleum Reserve, which government officials have said was an option to ease the pain of high oil prices on consumers.

It was not immediately clear why oil fell sharply in afternoon trade. After the sell-off, a White House official said "all options remain on the table, but we have nothing to announce at this time."

"As we have also said for some time, the administration continues to take steps to expand domestic oil and gas production, which has increased each year the president has been in office," the official said. "In fact, U.S. oil production is currently at an eight-year high, and domestic natural gas production is at an all-time high.”

CME Group, the parent company of the New York Mercantile Exchange, said it was not immediately aware of any technical issues that might have triggered a sharp sell-off in U.S. crude oil futures on Monday afternoon, a CME spokesman said.

The entire crude complex on CME [CME 58.71 -0.18 (-0.31%) ] Globex including crude oil, RBOB, gasoline and heating oil, "saw a coordinated sell-off of a prolonged duration of 30-minutes" from around 1:50 p.m. EDT to around 2:20 p.m. EDT on Monday, the spokesman said.

"I've been doing this for 14 years and that's the fastest move I've ever seen,'' said John Gretzinger, energy risk manager at INTL-FCStone in Kansas City. "I think it was too fast to be anything but HFT (high-frequency trading) or other algos. We just don't know right now, but that's my gut feeling.''