Whether you are shopping for a new car or just trying to maintain the one you have, you can take some steps to get the best mileage out of your gas purchases.

On the Road: Drive More Efficiently

1. Stay within posted speed limits. Gas mileage decreases rapidly at speeds above 60 miles per hour.

2. Stop aggressive driving. You can improve your gas mileage up to five percent around town if you avoid "jackrabbit" starts and stops by anticipating traffic conditions and driving gently.

3. Avoid unnecessary idling. It wastes fuel, costs you money, and pollutes the air. Turn off the engine if you anticipate a wait.

4. Combine errands. Several short trips taken from a cold start can use twice as much fuel as one trip covering the same distance when the engine is warm.

5. Use overdrive gears and cruise control when appropriate. They improve the fuel economy of your car when you're driving on a highway.

6. Remove excess weight from the trunk. An extra 100 pounds in the trunk can reduce a typical car's fuel economy by up to two percent. Avoid packing items on top of your car. A loaded roof rack or carrier creates wind resistance and can decrease fuel economy by five percent.

At the Garage: Maintain Your Car

7. Keep your engine tuned. Tuning your engine according to your owner's manual can increase gas mileage by an average of four percent. Increases vary depending on a car's condition.

8. Keep your tires properly inflated and aligned. It can increase gas mileage up to three percent.

9. Change your oil. According to the U.S. Department of Energy (DOE) and Environmental Protection Agency (EPA), you can improve your gas mileage by using the manufacturer's recommended grade of motor oil. Motor oil that says "Energy Conserving" on the performance symbol of the American Petroleum Institute contains friction-reducing additives that can improve fuel economy.

10. Check and replace air filters regularly. Replacing clogged filters can increase gas mileage up to ten percent.

At the Pump: Use the Octane Level You Need

11. Your owner's manual recommends the most effective octane level for your car. For most cars, the recommended gasoline is regular octane. In most cases, using a higher octane gas than the manufacturer recommends offers no benefit. Unless your engine is knocking, buying higher octane gasoline is a waste of money.

In Advertising: Check Out Claims About "Gas-Saving" Gadgets

12. Be skeptical of claims for devices that will "boost your mileage by an extra 6 miles per gallon," "improve your fuel economy up to 26 percent," or the like. The EPA has tested over 100 supposed gas-saving devices -- including mixture "enhancers" and fuel line magnets -- and found that very few provide any fuel economy benefits. The devices that work provide only marginal improvements. Some "gas-saving" devices may damage a car's engine or increase exhaust emissions.

In the Showroom: Consider the Alternatives

13. Alternative Fuel Vehicles (AFVs) operate on alternative fuels, such as methanol, ethanol, compressed natural gas, liquefied petroleum gas, electricity, and others. Using these alternative fuels in vehicles may reduce harmful pollutants and exhaust emissions.

14. Government Rules require labels on all new AFVs to give the vehicle's estimated cruising range and general descriptive information. Find out how many miles a new AFV travels on a tank or supply of fuel because, gallon for gallon, some don't travel as far as gasoline-powered vehicles.

15. Hybrid Electric Vehicles offer another option for car buyers. These vehicles combine the benefits of gasoline engines and electric motors and can be configured to achieve different objectives, such as improved fuel economy and increased power.