Gasoline prices remain lower than a year ago, but have bottomed out and are on the rise again, an analyst told the Associated Press. Trilby Lundberg said the prices have tumbled since peaking on May 18, when the average of all grades and taxes, as determined in a survey of 8,000 service stations in the United States, was $1.76 per gallon. Although the biggest trucks use diesel fuel, many commercial trucks operate on gasoline. Lundberg said the decline was caused by refiners overproducing to compensate for tight supplies in the spring. They have hit bottom in some locations and the price of regular gas in Chicago has risen 5 cents per gallon over the past few weeks.