Crude-oil futures tumbled nearly 5% Monday, extending their steep losses from last week, as traders locked in gains amid worries that a slowdown in the U.S. economy will lower demand for oil. Crude for September delivery ended down $ 3.42, or nearly 5%, at $ 72.06 a barrel on the New York Mercantile Exchange. That was the contract's lowest closing level since July 3. Reformulated gasoline and heating oil futures also declined sharply.

On Friday, crude futures finished with a loss of 1.8%, or $ 1.38, for the session, at $ 75.48 a barrel. The contract had climbed to an intraday high of $ 78.70 on Wednesday, the highest level a benchmark contract on the Nymex has ever seen. The benchmark contract marked a record closing high of $ 78.21 on Tuesday.

Other energy prices also fell sharply on Nymex Monday. September reformulated gasoline fell 10.31 cents, or nearly 5%, to finish at $ 1.9259 a gallon, its lowest closing level since March 23. September heating oil closed down 9.47 cents, or more than 4%, at $ 1.9393 a gallon. Falling oil also gave a boost to stocks. The Dow soared 286.87, or 2.18%, to 13,468.78. The Nasdaq composite index rose 36.08, or 1.44%, to 2,547.33.

Gold prices fell, while the dollar moved in a mixed range against other major currencies.