Because ethanol has lower energy density than gasoline, what is the typical effect on vehicle fuel economy when using ethanol blends?

• A. Higher Fuel Economy.
• B. Lower Fuel Economy.
• C. No Change.
• D. Fuel Economy Is Unrelated.

Answer: (B)

The main idea is energy density: ethanol stores less energy per gallon than gasoline. Because of that, when you run a vehicle on ethanol blends, the engine must burn a larger volume of fuel to deliver the same amount of energy. The result is fewer miles driven per gallon, i.e., lower fuel economy. The drop is small for low-percentage blends (like E10) and larger for high-percentage blends (like E85), but the overall trend is a decrease in MPG with ethanol blends.