Oil prices tumble

NEW YORK (CNNMoney.com) - Oil prices plummeted by the second-largest margin on record Tuesday as investors feared a further decline in U.S. demand after hearing comments from Federal Reserve Chairman Ben Bernanke.

Light, sweet crude fell $6.44 to settle at $138.74 a barrel in trading on the New York Mercantile Exchange.

The drop in oil was the largest single-day slide in dollar terms since January 17, 1991, when oil fell by $10.56. On that day, President George H.W. Bush withdrew oil from the Strategic Petroleum Reserve ahead of the first Gulf War. But in 1991, oil was trading at just $32 a barrel, so the $10.56 slide represented a record 33 percent drop. Oil fell 4.4 percent Tuesday, which does not even crack the top 100 price declines in percentage terms.

–By CNNMoney's Kenneth Musante and David Goldman