NEW YORK (AP) -- Oil prices tumbled more than $6 a barrel Friday -- the biggest one-day percentage plunge in nearly four years -- after a rebounding dollar and a Russian troop pullback in Georgia sparked another frenzied sell-off.

Crude's nosedive wiped out all the gains from the previous day's big rally and reaffirmed the belief that high energy prices and a softening global economy are still cutting into consumer demand for fossil fuels in the U.S. and overseas.

Light, sweet crude for October delivery fell $6.59, or 5.43 percent, to settle at $114.59 a barrel on the New York Mercantile Exchange.

It was crude's largest single-day price drop percentage-wise since Dec. 27, 2004, when prices dropped 6.47 percent. In dollar terms, it was oil's steepest one-day slide since Jan. 17, 1991, just after the start of the Gulf War. Crude prices had risen for three straight days, including an almost $6 rally on Thursday.

"This is extreme volatility," said Jim Ritterbusch, president of energy consultancy Ritterbusch and Associates in Galena, Ill. "The fact that we erased all of yesterday's gains so fast suggests that we're still in a bear market. There's just not much demand out there."

At the pump, a gallon of regular fell another penny overnight to a new national average of $3.692, according to auto club AAA, the Oil Price Information Service and Wright Express. Prices had peaked at

JACKSON, Wyo. (AP) -- Federal Reserve Chairman Ben Bernanke said Friday the financial crisis that has pounded the country -- coupled with higher inflation -- is taking a toll on the economy and poses a major challenge to Fed policymakers as they try to restore stability.

"Although we have seen improved functioning in some markets, the financial storm that reached gale force" around this time last year "has not yet subsided, and its effects on the broader economy are becoming apparent in the form of softening economic activity and rising unemployment," Bernanke said in a speech to a high-profile economics conference here.

While Bernanke welcomed the recent drops in oil and other commodities' prices, and believes inflation will moderate this year and next, the Fed chief also warned the inflation outlook remains highly uncertain.

The Fed, he said, would monitor the situation closely and will "act as necessary" to make sure that inflation doesn't get out of hand.

The current financial and economic environment is one of the most challenging to Fed policymakers "in memory," he acknowledged.

Given those dueling economic cross-currents-- weak economic growth and higher inflation -- many economists believe the Fed will leave rates where they are at its next meeting on Sept. 16, and probably through the rest of this year.

"They won't act until the coast is clear on financial stability and the state of the economy," said Allen Sinai,