The relationship between gallons used over a given distance and miles per gallon (mpg) is not linear. For example, replacing a truck that gets 10 mpg with one that gets 15 mpg will save 33 gallons of fuel for every 1,000 miles driven. In contrast, replacing a 30-mpg car with a new car that gets 35 mpg will save 5 gallons of fuel for every 1,000 miles driven.
Note: Each category on the horizontal axis shows a five-mile per gallon improvement in fuel economy.
Source: Oak Ridge National Laboratory, Transportation Energy Data Book: Edition 40, ORNL/TM-2022/2376, Figure 4.3. [Original source: U.S. Department of Energy fuel economy data.]