Exchange traded funds (ETFs) that consistently found themselves at the head of the class with double-digit returns in the first half of the year are suddenly having a different view of things as fuel prices continue their descent.

The price of gas has dropped for 25 consecutive days, and the average for a gallon on Friday was $3.85, reports the Associated Press. The cheapest gas can be had in Tulsa, Okla., where a gallon costs $3.50. Anchorage, Alaska, has the priciest, at $4.37. Prices are still $1 more than they were a year ago, says CNN Money.

In early trading today, oil is near the $115 mark. That’s despite the increasing hostilities between Russia and Georgia in the Caucasus region, which is a key transit route for oil and gas from the Caspian, reports Alistair Sharp for Reuters. Since July 11, oil has lost 21% of its value.

Natural gas isn’t immune, either, as futures have fallen 9.2% in just two weeks, says Ben Casselman for the Wall Street Journal. Production of the fuel is way up at 8% this year, and the growth is expected to continue in line with demand, which is up 5.5% this year through May.

Some analysts are talking about a “gas glut,” which in the short term could lead to lower heating and cooling bills. But the effect could be temporary, because if natural gas closes below $8 per million BTU, production will be scaled back – thus sending prices back up again.

ETFs that could continue to be affected by the drop-off in fuel prices include:

• iPath DJ-AIG Natural Gas Total Return Sub Index (GAZ), up 6.9% year-to-date
• PowerShares DB Oil Fund (DBO), up 25% year-to-date
• United States Natural Gas (UNG), up 7% year-to-date
• United States Gasoline (UGA), up 6.4% since April 18 inception

Tags: DBO, Eastern Europe, Energy, GAZ, Natural Gas, Oil, Russia, UGA, UNG