gas mileage vs fuel consumption rate

gas mileage and fuel consumption rate both are nouns.

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

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

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

Other synonyms of gas mileage include gasoline mileage, mileage.

gas mileage (noun)	fuel consumption rate (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