With the escalating price of gas, buying a fuel-efficient car makes a lot of sense. Approximately 15% of new car buyers reject a model due to poor gas mileage. Nearly 40% of those consumers who eliminate a full-size SUV due to gas mileage ultimately purchase a midsize SUV instead, while nearly 20% purchase another model altogether. (J.D. Power and Associates, Sept. 2004.)

But even if you don't currently own a fuel-efficient car, there are lots of ways you can improve the fuel efficiency of your present vehicle until you're ready to purchase one of the best gas mileage cars. Your personal driving habits have a big effect on your fuel use and costs. You can better manage your vehicle operating costs as well as minimize the emissions it produces by driving less and more efficiently. Here are some tips to help. First, you need to know what kind of mileage you are getting. Calculate this by filling up your tank and recording the odometer reading-or you can reset your trip gauge to zero. Next time you get gas, fill the tank again and divide the miles you traveled between fill ups by the quantity of gas you bought on this fill-up. This is your car's miles per gallon or mpg. If it's pretty dismal, here's how to turn your fuel guzzler into a fuel saver: Drive slower: The aerodynamic drag on your car increases noticeably the faster you drive. The drag force at 70 mph is about double that at 50 mph, so keeping speed down can increase your mileage considerably. Gas mileage decreases rapidly at speeds over 60 mph. Each 5 mph above 60 mph is like paying an additional $.10/gallon for gas. Observing the speed limit is also safer for everyone.

Maintain a constant speed: Every time you speed up, you use energy, some of which is wasted when you slow the car down again. By maintaining a constant speed, especially driving the posted speed limit, you will improve your fuel efficiency. Just by increasing your highway cruising speed from 62 mph to 74 mph you increase fuel consumption by about 20%! Using cruise control on the highway helps you maintain a constant speed and will usually save gas.

Drive gently: Aggressive driving-speeding, rapid acceleration and hard braking-wastes gas. These bad habits can lower your gas mileage by 33% at highway speeds and 5% in the city. In addition, reasonable driving is safer for you and others, so you may be saving more than gas money. Consider using overdrive gears on the highway, as this decreases engine speed, reducing fuel usage and engine wear.

Avoid Excess Idling: Idling gets 0 miles/gallon and wastes fuel and money, is hard on the engine and adds to toxic emissions. Cars with larger engines typically waste more gas at idle than those with smaller engines. Turn off your engine if you think you will be stopped for more than 30 seconds. However, if you're driving a fuel-efficient car like a hybrid, your electric motor is on when you idle, so you're not wasting any gas at all! Minimize air conditioning: Using your air conditioner in hot weather can increase your fuel consumption by more than 20% in city driving. Whenever possible, close all windows and use the air vents to circulate air instead of air conditioning. You will improve your fuel efficiency in summer by minimizing the use of air conditioning and using your car's flow-through ventilation, especially on the highway. If you must use the air conditioning, set the controls to a level that lets the system cycle, and turn it off once the interior of car is cooled down enough. Also consider such options a sunroof and tinted glass to keep the car cool.

Keep Your Car in Shape: Maintaining your vehicle in top working condition saves you fuel and money, and reduces long-term maintenance costs while minimizing harmful emissions.

Keep Your Engine Properly Tuned-Getting regular tune-ups when your car is out of tune or has failed an emissions test may improve gas mileage by about 4%. If your car has a faulty oxygen sensor and you have it fixed, gas mileage could improve as much as 40%. Make sure the spark plugs, if you have them, are firing properly, replacing them when necessary. Have the engine timing checked for accuracy.

Check & Replace Air Filters Regularly-Replacing a clogged air filter could improve a car's gas mileage by as much as 10%. Additionally, it will protect your engine from impurities. Change this more often if you live in a dusty climate, drive on dirt or gravel roads or if you drive off-road for fun.

Keep Tires Properly Inflated-Your gas mileage can increase by about 3.3% if you keep tires inflated to their proper pressure. It takes more effort and gas for the engine to propel an underinflated tire than a correctly inflated one-which provide less road-resistance, thereby improving fuel efficiency. Beware over-inflation, though, which can lead to handling problems and uneven tire wear. Check tire pressure on a regular basis, looking for signs of uneven wear or embedded objects that can cause air leaks. In winter, check tire pressure if there is a sharp change in temperature, as cold weather decreases air pressure in the tires. Use the Recommended Grade of Motor Oil-Fuel efficiency can improve by 1-2% if you use the manufacturer's recommended grade of motor oil. Also, if you change your own oil, look for motor oil rated as "Energy Conserving" to be sure it contains friction-reducing additives.

Check Which Gas to Use-Choose the correct octane gas for your car by checking your owner's manual. It's not necessary to buy the "super" high-octane gas unless your car manufacturer recommends it or your engine knocks without it. While you won't do harm to the engine, you will be paying more than you need to, since premium (highest octane) gas sells for an average of 17 cents more per gallon than regular gas. Only about 6% of cars sold in the U.S. need premium gas, according to the AAA. Also, avoid topping off your gas tank, since in warmer weather, fuel expansion can cause an overflow and you'll be wasting precious fuel. You want to be a fuel saver-not a fuel waster!

Planning & Combining Trips: Combining errands to do together and in similar areas saves time and money. Several short trips starting from a cold engine can use twice as much fuel as a longer multi-purpose trip that covers the same distance when the engine is warmed up. With a little advance planning, you can avoid high traffic areas, road construction, retracing your route and ultimately reduce the distance you travel while running errands. You'll not only save on fuel, but also reduce wear and tear on your car. Commuting: If you can alternate your work hours to avoid rush hour, you'll spend less time sitting in traffic and burn up less fuel. For stop and go traffic, drive your best gas mileage car if you own more than one vehicle. Contemplate telecommuting (working from home) when your job permits. If you can, participate in carpools and ride-share programs. You can cut your weekly fuel costs in half and save wear on your car if you take turns sharing driving with others.

Traveling: A roof rack or carrier affords additional cargo space and helps out when you have a smaller car. However, a loaded roof rack decreases fuel efficiency by 5%. Reduce the wind resistance and increase your fuel efficiency by putting objects inside the trunk when possible. Also, remove any unnecessary items, especially heavy ones, as an extra 100 lbs. in the trunk reduces a car's fuel efficiency by about 1 to 2%.