Oil prices slumped in early Asian trading after voting ended in a British referendum on whether to stay in the European Union, with early returns showing the "Leave" camp holding the lead.
U.S. crude was down $1.54 at $48.58 a barrel at around 0117 GMT (9:17 p.m. ET). Brent crude was down $1.47 at $49.44 a barrel. Both fell more than $2 a barrel at one point.
On Thursday, both contracts rose sharply, rallying on optimism that Britons would vote to stay in Europe.
"It's like a rollercoaster ride in the markets right now, but it's too early to tell which side is going to win," said Bob Takai, president at Sumitomo Corp Global Research.
Early results from Britain's bitterly contested referendum showed a lead on Friday for supporters of leaving the European Union, contradicting opinion polls.
Sterling dropped as far as $1.4300 at one stage, having risen to a high for the year at $1.5022. It was last at around $1.4550 in its biggest intraday fall since May 2010.
The euro fell to $1.1312 while the yen recouped early losses to stand at 105.14 per dollar.
