Average retail gasoline prices jumped more than a penny-a-gallon during the past two weeks nationwide and motorists can expect the increases to continue, an analyst said. The 1.18 cent-a-gallon increase for all grades of gasoline pushed the average price to 96.14 cents in the period ended April 8, according to the Lundberg Survey. Wholesale prices increased at twice the retail rate, analyst Trilby Lundberg said Sunday. ``This means retailers lost a penny of their operating margin during the period and it means that there is more price pressure to come in the immediate future,'' she said. According to the survey, prices per gallon at self-service pumps were: regular unleaded, 86.80 cents; premium unleaded, $101.84; regular leaded, 83.97 cents. Prices at full-service pumps were: regular unleaded, $116.93; premium unleaded, $127.20; regular leaded, $112.51.