Source: U.S. Energy Information Administration, Annual Energy Outlook 2014 Note: Calculations in graphic assume a fuel price of $3.50 per gallon and annual travel of 12,000 miles per vehicle.
Fuel costs, which depend on vehicle fuel economy, miles driven, and fuel price, are an important factor in vehicle purchasing decisions. However, fuel economy improvement exhibits diminishing returns in fuel savings. For example, switching from a 10-mile-per-gallon (mpg) vehicle to a 15-mpg vehicle saves more fuel and results in greater fuel cost savings than switching from a 25-mpg vehicle to a 75-mpg vehicle. The fuel and cost savings of improving fuel economy from 12 mpg to 15 mpg are the same as increasing from 30 mpg to 60 mpg.
Much of the reduction in fuel consumption and fuel cost comes from incremental fuel economy improvement at the relatively low fuel economy levels. For a consumer who drives 12,000 miles per year and pays $3.50 per gallon for gasoline, increasing fuel economy from 10 mpg to 11 mpg saves $382 in annual fuel cost and from 30 mpg from 31 mpg saves $45; raising fuel economy from 40 to 41 mpg saves just $26 and from 60 to 61 saves $11.
Vehicles that use fuels other than gasoline, such as diesel or electricity, will have different fuel savings and fuel cost. Diesel vehicles often have higher fuel economy than standard gasoline vehicles, but they also must use diesel fuel, which is more expensive than gasoline. Plug-in electric vehicles, which achieve high fuel efficiency and take advantage of relatively inexpensive electricity (compared to gasoline), can accrue significant fuel cost savings, albeit at higher incremental vehicle cost.