Kelley Blue Book, which provides price information on new and used vehicles, said today that the values of fuel-efficient vehicles are likely to drop 15 percent by year’s end, due largely to stabilizing fuel prices and a return to normal production schedules for Japanese manufacturers. After 20 weeks of consecutive gains, values for gas-sipping vehicles peaked in May in response to a decline in fuel prices. During the past four to six weeks, values of compacts and subcompacts declined approximately 1 to 2 percent, along with the overall market. Kelley’s valuation team expects the overall used-vehicle market to decline no more than an additional 3 to 5 percent between now and the end of the year.