Crude oil prices tumbled anew Friday as fears built that economies around the world are slowing, which will lead to weaker demand for petroleum products. Recently, light, sweet crude was down $6.91 in New York to $79.68 a barrel, putting the contract 45% below its all-time high near $148, reached less than three months ago. Brent crude was losing $4.51 to $78.15 a barrel. Heating oil was down 18 cents to $2.24 a gallon, and gasoline futures were falling 18 cents to $1.84 a gallon. Natural gas was lower by 11 cents at $6.72 per million British thermal units. Stocks in the energy sector were falling hard. Exxon Mobil ( XOM) and ConocoPhillips ( COP) were each losing more than 10%, and Chevron ( CVX) was weaker by 7%. BP ( BP) was down 4%, and Royal Dutch Shell ( RDS.A) gave back 6.8%. The US Oil ( USO) ETF, which tracks crude prices, was shedding 6.2%.