The month-old rally in U.S. retail gasoline prices has fizzled, analysts said.

"There was a point in September when refineries were making as much as $20 to $25 on a barrel of product," said Tom Kloza, senior oil analyst for the Oil Price information Service in New Jersey. "Now, the average profit is about $2.50 a barrel. It's going to be a very challenging next few months for refiners."

After four consecutive weeks of modest gains, the national average fell 2.8 cents this past week to $2.666.

This is despite major gasoline producers such as Sunoco Inc., Valero Energy Inc. and Flying J doing extended maintenance on some of their plants. Some of the nation's biggest refineries have been shut down indefinitely as demand for fuel remains very weak in the midst of the U.S. economic downturn.

Nonetheless, the government said Tuesday that oil prices should average about $77 a barrel this winter, 10 percent more than its estimates issued just last month.

Oil prices have jumped about $10 per barrel in the same time period.

The Energy Information Administration forecast is based on the assumption that the world economy would continue to pull itself out of recession, and U.S. GDP would grow by 1.9 percent next year. It said oil prices should continue to climb to $81 a barrel by December 2010.

Because oil is largely bought and sold in U.S. currency, it effectively becomes cheaper if the dollar falls. Investors holding stronger currencies like the euro can trade them in for dollars and buy more oil.

Rising oil prices force other energy commodities higher. Gasoline, heating oil and diesel have all followed crude higher.

The EIA said it expects the national average gas prices to rise from $2.55 per gallon in October to $2.70 per gallon this month. Pump prices are estimated to rise to an average of $2.81 in 2010, with prices increasing to $3 a gallon during the summer driving season.