If you've been kicking around the idea of buying or leasing a new SUV and upgrading to a more fuel-efficient model, it's important to know that you may not be comparing apples and apples. This year marked a change in how the Environmental Protection Agency (EPA) determines how the fuel economy of brand new 2008 cars, pick uppickup trucks, and SUVs is calculated.

Prior to 2008, the EPA, along with automobile manufacturers, used a method of testing a vehicle's ratings that let's just say, didn't adequately recreate real-world conditions. The vehicle was placed on a set of rollers called a 'dynamometer' that allowed the car to sit in place while turning the wheels of the vehicle. Although the drag on the rollers was adjusted to better simulate various driving conditions, the vehicles were never tested in environments where wind resistance could influence the amount of fuel being burned, and the accessories were never running. Hence, the test created a level playing field for all vehicles of the same class to be compared, but the results never depicted the fuel economy you could expect in the real world. In addition, the simulated speeds prior to 2008 were considerably slower than what the average driver actually drives ? only 48 miles per hour for highway tests and 20 miles per hour for tests in the city.

Starting this year, the EPA has begun to use an adjusted system of testing requirements to account for all the things that affect fuel economy: faster acceleration, higher speeds in both the city and on the highway, colder external temperatures, and vehicles are now tested with accessories (like the air conditioning) on.

The result? While the new method of testing gives potential buyers a better idea of what they can expect when the vehicle is driven off the lot, overall mileage projections have been reduced. While most people would probably prefer a more accurate method of testing, and therefore more accurate results, the problems arise when we throw another ingredient into the mix. Many automobile manufacturers have upgraded their 2008 lines to be more fuel-efficient as a response to increased gas prices over the past two years. Unfortunately, on paper, these vehicles now appear to be less fuel fuel-efficient than their predecessors. Without an understanding of the new testing system, comparing one's older model to a new 2008 could suggest you're better off keeping the car or pick uppickup truck you have. Chances are, you're not. Even the "non-green" models (models that still operate solely on unleaded gasoline without the assistance of an electrical power source) are becoming increasingly economical.

For example, the popular 2008 Isuzu Ascender advertises a fuel economy of 14 miles per hour gallon in the city and 20 on the highway. At first glance, that might seem lower than the ratings you're used to seeing. In reality, it's right in line with other 2008 midsize SUVs in the Ascender's class; the Ford Explorer, Mercury Mountaineer, GMC Envoy, and Chevy Trailblazer all share the same rating. The 2008 Jeep Grand Cherokee and Hummer H3 both rate slightly lower than the Ascender under the new, more accurate tests. Although the numbers will say that this year's Ascender get fewer miles per gallon than last year's, that's not true. The 2008 4.2-liter, six-cylinder engine has actually been recalibrated for efficiency and according to Consumer Guide, accelerated to 60 mph in 8.8 seconds.

The moral of the story? Comparing '08 models to previous years won't tell you much in terms of fuel economy, so stick to comparisons between the newest models to gauge if the SUV or car you've got your eye on stands up to others in its class.