June 19 (Bloomberg) -- The U.S. would achieve bigger fuel savings by focusing more on eliminating gas-guzzling autos than on shifting drivers from moderately efficient vehicles into the most-economical models, according to a study released today.

Replacing a vehicle getting 18 miles per gallon of gasoline with one getting 28 mpg, for example, may lead to 198 gallons (750 liters) in fuel savings per 10,000 miles, twice the benefit of a switch from a 34-mpg auto to a 50-mpg model, said the researchers from Duke University in Durham, North Carolina.

``People underestimate the value of removing the most fuel- inefficient vehicles,'' Professors Richard Larrick and Jack Soll of Duke's Fuqua School of Business wrote. ``Removing the most inefficient vehicles is where policy and popular opinion should be focused.''

Larrick and Soll said automakers and the U.S. Environmental Protection Agency should consider changing their vehicle ratings to show gallons of gasoline consumed per 100 miles, rather than miles per gallon, to better serve consumers.

With such a system, buyers can easily calculate the cost of a given trip and compare that with other vehicles relative to their price tags, the study concluded.

Autos with the highest fuel efficiency are still of greatest benefit to the environment over the life of the vehicle, when compared with cars and trucks that consume more gasoline, the study's authors said.

As a result, automakers should tie incentive offerings to the greenest vehicles in their portfolios to encourage consumers to consider buying them, Larrick and Soll said.

To contact the reporter on this story: Greg Bensinger in New York at gbensinger1@bloomberg.net

Last Updated: June 19, 2008 16:00 EDT