As the traditional peak season for gasoline demand winds down, pump prices are all fired up —now exceeding year ago levels.
The national average price for regular unleaded gasoline rose a penny to $3.66 a gallon on Thursday, according to the American Automobile Association, up a penny from $3.65 a gallon this time last year. On average, gasoline prices have surged 8 percent in the past month alone.
"All markets have increased since late June, but the latest spurt has come on the heels of a cluster of refinery issues in the Midwest, and more recently, the explosion and fire at a key Chevron facility in the Bay area," says OPIS analyst Tom Kloza. (Related: US Midwest Hit by Perfect Storm on Gas Prices.)
California retail gasoline has advanced throughout the week and the average Golden State number this morning is $3.93 a gallon, up 14 cents from a year ago.
Most of the other large year-on-year increases are in the upper Midwest. Average prices in Illinois are $4.03 a gallon, a 19 cent jump from a year ago; Michigan unleaded is $3.96, up 24 cents; Ohio has advanced to $3.80, reflecting an increase of 22 cents from last year; and Wisconsin prices are at $3.91, up 24 cents from the same date in 2011.
"In all, 19 states now find regular unleaded at a higher price than Aug. 9, 2011," Kloza says. "More than half of the country may see year-on-year increases by mid-month."
The year-on-year increase list already includes political "battleground" states such as Colorado, Iowa, Minnesota, Missouri, Ohio, and Wisconsin, Kloza says, and it could soon include Nevada, Virginia, and North Carolina, he adds.
Year-to-date, the average price for regular unleaded gas is $3.61 a gallon. Throughout all of 2011, drivers paid on average $3.51 a gallon, making it the most expensive year on record, according to OPIS.
—By CNBC's Sharon Epperson. Follow Sharon on Twitter: @sharon_epperson