Oil markets: Bottoming out or taking a breather?

The declines accelerated amid growing concerns that the weakening economy and creeping inflation are eroding demand for fossil fuels in the U.S. and other large energy-consuming nations.

Oil is now more than 10 percent cheaper per barrel than it was on Monday; natural gas prices are down more than 20 percent just since the Fourth of July. Still, experts are not convinced that prices have turned a corner.

"There's no bell that tells you when the market has turned," said James Cordier, president of Tampa, Fla.-based trading firms Liberty Trading Group and OptionSellers.com.

Light, sweet crude for August delivery dropped $5.31 to settle at $129.29 a barrel on the New York Mercantile Exchange. Prices have fallen nearly $16 in just the past three days.

Natural gas futures for August delivery fell more than 8 percent Thursday, marking their biggest one-day drop in nearly a year, according to Nathan Golz, researcher at Wachovia Securities in St. Louis. Prices for the key heating, cooking and power generation fuel settled 86.1 cents lower at $10.537, their lowest point since April.

A number of market observers say there simply wasn't enough support for the recent run up in natural gas prices, and that this week's sell-off of oil has only helped speed the declines.

"Any time oil goes up or down on Nymex, it's going to have a carry-over effect on natural gas," said Michael Rieke, senior managing editor for power and gas at energy research firm Platts.

The immediate cause of Thursday's sharp natural gas decline was a larger-than-expected increase of U.S. supplies.

The Energy Department's Energy Information Administration said in its weekly report that natural gas inventories rose by 104 billion cubic feet to more than 2.31 trillion last week. Analysts had been expecting supplies to grow by only 86 billion to 91 billion cubic feet, according to a Platts survey.