The national average for self-serve, regular unleaded gasoline was about $1.6622 a gallon on December 19, down some 9.04 cents from two weeks earlier, according to the nationwide Lundberg survey of 5,000 gas stations in metropolitan areas.

That is less than half what consumers paid in July when the average price reached an all-time high of $4.11 a gallon. It is also $1.31 per gallon less than the average price paid this time a year ago.

High gas prices over the past year have crimped demand, hurting producers and retailers, but the economy will get a boost from the drop in prices, survey editor Trilby Lundberg told Reuters.

"It is extremely healthy that we have had a crash, which will help (economic) recovery," she said.

Lundberg added that current gas prices, which have come down in tandem with crude oil prices, reflected some normalization in retail margins.

For gas stations, retail margins reached the highest-ever annual average in 2008 at nearly 15 cents on the gallon, while oil refiners' margin of 29 cents per gallon was the lowest since 2002, Lundberg said.

The average price for a gallon of unleaded gasoline in 2008 was $3.23, while through December 19, the average price for a barrel of crude oil was $98, Lundberg said.

A barrel of U.S. crude hit $147 in July, the highest-level ever. At Friday's close, crude oil on the New York Mercantile Exchange, or NYMEX, fell to $33.87 a barrel.

Lundberg said that in the United States about 15 percent of refinery capacity is currently out of operation.

"In addition to a lot of the idled gas production ... some refiners are undergoing maintenance to prepare for spring" when demand for gasoline generally rises, Lundberg said.

At $2.41 a gallon, Anchorage, Alaska, had the highest average price for self-serve, regular unleaded gas, while the lowest price was $1.37 a gallon in Cheyenne, Wyoming.

Excluding Alaska and Hawaii, where gas prices tend to be higher, Lundberg said it was now most expensive to fill up at pumps in Long Island, New York, where the average price was $1.92 for a gallon of regular gasoline.

(Reporting by Lilla Zuill, editing by Maureen Bavdek)