Motorists are paying the highest prices for gas since October 2008. Retail gasoline prices rose on Thursday on an expected increase in demand and as more expensive spring and summer blends of gasoline make their way to the pumps. The nationwide average hit $2.799 per gallon, a penny higher than Wednesday, according to AAA, Wright Express and Oil Price Information Service. Prices have now jumped 18.9 cents in the past month and are 87.9 cents higher than year-ago levels. Back on Oct. 23, 2008 prices averaged $2.8215 per gallon.