U.S. light crude for May delivery jumped $5.18, or 12 percent, to $68.91 a barrel in electronic trading.
Both Reuters and one trader said the spike wasn't an electronic glitch, but what was causing the jump wasn't known.
The trader said various rumors were circulating in the market, including that Iran had fired on U.S. warships and that British commandos had mounted a rescue attempt of its captured sailors, but nothing had been confirmed.
The White House said there is nothing to indicate any incident took place regarding Iran, Reuters reported.