mileage vs fuel consumption rate

mileage and fuel consumption rate both are nouns.

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

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

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

Other synonyms of mileage include gas mileage, gasoline mileage.

mileage (noun)	fuel consumption rate (noun)
distance measured in miles	the ratio of the number of miles traveled to the number of gallons of gasoline burned
a travel allowance at a given rate per mile traveled
the ratio of the number of miles traveled to the number of gallons of gasoline burned