The darkening gloom that hangs over the U.S. economy spread to the oil markets yesterday, sending the cost of crude tumbling $6.44 a barrel in the largest one-day plunge since 1991.

In a wild day of trading, the cost of light, sweet crude oil for August delivery closed at $138.74 a barrel on the New York Mercantile Exchange.

But before that moment of relative calm, prices see-sawed crazily during electronic and New York pit trading.

At one point, the difference between the day's highest and lowest oil trade exceeded $10.

Yesterday's decline represented the biggest dollar drop since January 1991, the beginning of Operation Desert Storm in Iraq.

Even at its most expensive yesterday, crude still fell short of the record high of $147.27 set July 11. The essential commodity has seen large price swings — both up and down — in recent weeks.

U.S. oil consumption has slumped amid soaring oil prices and gas prices over $4 a gallon.