(CNN) — U.S. gasoline prices have declined for four weeks straight and now average more than 20 cents a gallon cheaper than a year ago, according to a new nationwide survey.
The average cost of a gallon across the continental United States of regular stands at $3.71, down 3 cents from two weeks earlier, said Trilby Lundberg, publisher of the Lundberg Survey. Prices have fallen nearly 9 cents a gallon in the past four weeks and are 22 cents cheaper than at this point in 2012, Lundberg said.
Lower prices in the Europe’s benchmark Brent crude oil are largely behind the most recent fall. More U.S. refining capacity coming back on line after seasonal maintenance also contributed, Lundberg said.
“From there, short-term, we may see more price-cutting soon, perhaps on the order of this approximate 3-cent decline,” she said. “But the current picture suggests it won’t be large.”
Gas prices broke a three-month upward spiral in early March, which had climbed nearly 54 cents since late December.
The Lundberg Survey canvasses about 2,500 filling stations across the Lower 48 states every two weeks. The most expensive fuel in the latest survey, conducted Friday, was in Chicago, where pump prices averaged $4.10 a gallon; the cheapest could be found in Billings, Montana, at $3.33, Lundberg said.
Average per-gallon prices in other cities:
Baton Rouge, Louisiana: $3.45
Las Vegas: $3.72
Memphis, Tennessee: $3.43
San Francisco: $4.07
This article was written by CNN’s Matt Smith. TM & © 2012 Cable News Network, Inc., a Time Warner Company. All rights reserved.