Energy stocks plunged Friday as crude and natural gas prices dropped to levels not seen in more than a year.

The sector has fallen alongside a broader sell-off on Wall Street, with the Dow Jones industrials dropping nearly 700 points at one point Friday, or about 8 percent.

Consumers have already begun driving fewer miles and using less electricity to save money. The Department of Energy reported demand for gasoline over the past four weeks was down 5.3 percent.

On Friday, the International Energy Agency, a Paris-based energy watchdog agency, cut its forecast for oil demand this year by 240,000 barrels per day and 440,000 barrels per day for 2009.

“We are now seeing the final death throws of the bubble that was built into this market,” said Stephen Schork, a commodities analyst and trader.

On the New York Mercantile Exchange, light, sweet crude for December delivery fell $8.63, or 10 percent, to settle at $77.99 per barrel. The breathtaking drop comes after prices for the fossil fuel hit an all-time high of $147.27 on July 11. Today’s close marks a 47 percent loss in value for a barrel of oil.

Meanwhile, natural gas for November delivery lost 29 cents, or 4 percent, to $6.825 per 1,000 cubic feet. Prices had traded above $10 in July.

Shares of Exxon Mobil Corp., one of the largest energy companies in the world, dropped nearly 13 percent, or $8.60, to $59.40. Shares hit a 52-week low of $57.19 earlier in the session.

Exxon reported the largest ever quarterly operating profit for a U.S. company in July _ $11.7 billion _ on the back of record crude prices.

With energy prices sinking, it’s not inconceivable that crude could hit $50 per barrel, said Schork.

“If you can go to the obscene number on the upside, you can certainly go to the obscene on the downside,” he said.

Shares of major refiners also got singed Friday. The sector was squeezed by the surge in crude prices this summer as it struggled to pass on higher energy costs to customers. But crumbling demand now means that refiners may do less business.

Shares of Tesoro Corp. fell $1.15, or 12.5 percent, to $8.05, and Marathon Oil Corp. dropped $3.19, or 11.6 percent, to $23.76.

Oilfield services companies, which help run exploration and production operations that are lucrative when crude prices are high, also took a big hit. Shares of National Oilwell Varco Inc. plunged $5.51, or 19.1 percent, to $23.25.

Elsewhere in the energy sector, shares of Hess Corp. slid $7.18, or 13.4 percent, to $46.32; shares of ConocoPhillips lost $6.30, or 11.7 percent, to $47.53. Shares of Chevron Corp. fell $5.29, or 8.3 percent, to $58.71.