According to the U.S. Department of Energy, diesel engines offer 30- to 35-percent greater fuel economy than comparable gasoline engines. Diesel fuel also has higher energy density than gasoline, which means less fuel is required to generate the same power as gas, improving overall fuel economy.

Typical mid-size vehicles might include a Pontiac Grand Am or a Nissan Altima. A full-size rental might include a Ford Taurus or a Chevy Impala. A mid-size vehicle with one rental car company may give you more room than a vehicle in the same class with a different company.

Maintain a checklist before heading out to purchase a used truck: History check Maintenance history Know why it is being sold Accident history Find out what has to be replaced Perform quality inspection Assess the mechanical functioning Plan and then make your purchase.