The average U.S. price of regular-grade gasoline shot up 16 cents a gallon over the past two weeks, to $2.66. Industry analyst Trilby Lundberg of the Lundberg Survey says the rise comes as supplies tighten while refineries undergo maintenance in advance of increased demand during the summer driving season. The lowest average is $2.29 in Baton Rouge, Louisiana. According to Triple-A, The highest average price in the nation is in Mono County at 4.36 a gallon. San Luis Obispo County reports 3.62 a gallon and 3.54 for Santa Barbara County.