An analysis by The Associated Press is raising questions about many of the deals made under the government's Cash for Clunkers program.

The idea of the program was to encourage motorists to trade in their gas-guzzling vehicles for more fuel-efficient ones. The government spent $3 billion to achieve that goal.

But the AP analysis of federal data found the most common deals under Cash for Clunkers involved replacing old Ford or Chevrolet pickups with new ones that got only marginally better gas mileage. The single most common swap involved Ford 150 pickup owners who traded their old trucks for new Ford 150s.

In at least 145 cases, mostly involving trucks, the government reported consumers bought new vehicles that had the same or worse mileage as the trade-ins.

The government says it's investigating these and other questionable deals.

Copyright 2009 by The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.