Despite the common belief that the government tests every new car’s fuel economy, the manufacturer is the one who performs the testing. They follow guidelines set by the Environmental Protection Agency (EPA). Miles per gallon (MPG) numbers are big business, and a small improvement over the competition can drive thousands of dollars in new sales. Manufacturers have a huge incentive to game the system to score the highest number. As a result, drivers often see huge variances in the quoted miles per gallon and what they actually get. Here’s how the system works and where you can look for real world MPG numbers.

CleanMPG is a website that keeps track of the real world mileage of hybrid, electric, and alternative fuel vehicles. Actual owners, making it easy to compare the cars in the real world, submit their MPG numbers. Additionally, CleanMPG offers driving tips to achieve the best MPG.

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Many cars have computers to display miles-per-gallon.

To compare window sticker EPA numbers, or actual numbers submitted by drivers, the government maintains FuelEconomy.gov. They have a database of every vehicle ever tested, and allow users to compare window stickers side by side. Government testing procedures are included for review, along with tips and tricks for driving.

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Hybrid vehicles can fluctuate wildly with MPG.

READ: 5 Free Gas Mileage Cheats

We have our own list of ways to achieve better mileage with any vehicle. Fuel mileage can be dramatically altered by the way the car is driven. Accelerating quickly or braking hard can lower the number dramatically. Removing unnecessary weight, especially from the trunk, will have a positive effect.

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Example of EPA mileage sticker on new cars.

READ: Hybrid or Diesel: What Should I Buy for the Best Fuel Economy?

If you are looking for the most fuel-efficient vehicle for driving around town, we recommend either a hybrid or full electric vehicle. For long distance commutes, a diesel-powered vehicle is the best choice.

Remember when looking at the EPA rating of a vehicle, the fuel economy listed may not be what you experience in the real world. Manufacturers advertise heavily on MPG, and have a lot invested in scoring a high number. When comparing vehicles, be sure to do some research in advance to see what people are getting in the real world.