Gov. Martin O'Malley wants to apply Maryland's 6 percent sales tax to gasoline, a change that at current prices would add 18 cents a gallon to the cost at the pump. The increase — to be phased in over three years — would be on top of the 23.5 cents per gallon gas tax the state has been charging since 1992. The change would require the approval of the Maryland General Assembly, where its prospects are uncertain. Read more about the gas tax proposal here. Above, a Shell gas station on Russell Street.Baltimore Sun/Gene Sweeney Jr.