fuel consumption rate vs gas mileage

fuel consumption rate and gas mileage both are nouns.

Word	Noun	Adjective	Verb	Adverb
fuel consumption rate	Yes	No	No	No
gas mileage	Yes	No	No	No

As nouns, fuel consumption rate and gas mileage are synonyms defined as:

fuel consumption rate and gas mileage: the ratio of the number of miles traveled to the number of gallons of gasoline burned

Other synonyms of fuel consumption rate include gasoline mileage, mileage.

fuel consumption rate (noun)	gas mileage (noun)
the ratio of the number of miles traveled to the number of gallons of gasoline burned	the ratio of the number of miles traveled to the number of gallons of gasoline burned