You look at the window sticker and it reads “35 mpg,” so you think to yourself – why, that’s great, perfect, a nice car with great gas mileage. Sold!

Not so fast. The numbers that more Americans are considering seriously when it comes to the purchase of a vehicle may not be very accurate. According to Autobytel’s own analysis of recent vehicles and a report from Consumer Reports, the EPA’s rated miles per gallon can be much greater than what you will get on the road, especially when it comes to hybrid vehicles.

According to Consumer Reports, they found that the EPA’s estimates ran 35 – 50 percent higher than the vehicle’s actual fuel efficiency. Hybrids averaged 19 miles per gallon less than their EPA ratings, according to the publication, and ratings were too low for 90 percent of the vehicles tested. Autobytel’s own road tests support these findings. For example, a road test in the Toyota Prius consistently registered a combined fuel economy of 45, compared to its listed EPA rating of 60/51, and the Ford Escape Hybrid registered just 25 combined city and highway miles per gallon – though the EPA fuel economy is listed at 31/27. Worse yet is the new Toyota Highlander, whose “real world” miles per gallon came in at 19.8, compared to a stickered EPA estimate of 31/27. The same holds true for traditional powertrains – though the difference is generally not quite so stark. Part of the reason for the difference lays in the laboratory approach the EPA uses to test its vehicles. According to fueleconomy.gov, “the vehicle's drive wheels are placed on a machine called a dynamometer that simulates the driving environment—much like an exercise bike simulates cycling. The energy required to move the rollers can be adjusted to account for aerodynamic forces and the vehicle's weight. On the dynamometer, a professional driver runs the vehicle through a standardized driving routine, or schedule, which simulates “typical” trips in the city or on the highway.”

Ask Lance Armstrong if a trip on an exercise bike closely approximates the experience of riding up the Alps. There are likely to be some pretty big differences, of course. But no matter what the reason, many car buyers will be unpleasantly surprised when they realize that they aren’t getting the kind of savings they thought they’d enjoy. And while the kind of fuel consumption you manage depends greatly on your driving style, the quality of the road and the types of traffic you encounter, the variance between rated miles per gallon and “real world” numbers makes a difference, especially with gas topping $3 a gallon.