WASHINGTON — The most common deals under the U.S. government’s $3 billion Cash for Clunkers program, aimed at putting more fuel-efficient cars on the road, replaced old Ford or Chevrolet pickup trucks with new ones that got only marginally better gas mileage, according to an analysis of new federal data by The Associated Press.

The single most common swap — which occurred more than 8,200 times — involved Ford 150 pickup owners who took advantage of a government rebate to trade their old trucks for new Ford 150s. They were 17 times more likely to buy a new F150 than, say, a Toyota Prius. The fuel economy for the new trucks ranged from 15 mpg (6.3 kpl) to 17 mpg (7.2 kpl) based on engine size and other factors, an improvement of just 1 mpg (0.43 kpl) to 3 mpg (1.2 kpl) over the clunkers, or old vehicles. .