Some consumers may notice that their fuel economy estimates differ from EPA's estimates. This is not unusual, since real-world conditions frequently differ from those in laboratory tests, which are strictly controlled so that the results can be used to compare the fuel economy of different vehicles:

• No laboratory test can simulate all driving conditions and driving styles. Trip length, traffic conditions, terrain, temperature, and weather all affect fuel economy. In addition, fast acceleration and heavy braking, driving at high speeds, carrying extra weight, using cargo racks, using electrical accessories, and using 4-wheel drive reduce fuel economy.

• Vehicle maintenance can affect fuel economy. Test vehicles are typically in optimum condition.

• Fuels vary in energy content. Oxygenated and reformulated gasoline contains less energy per volume, and gasoline composition varies seasonally.

• Small differences due to vehicle manufacturing and assembling can cause differences in fuel economy.

• New vehicles don’t attain maximum fuel economy until they’re “broken in,” usually around 3-5 thousand miles.

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