"Mileage requirements" refers to the specific distance that a vehicle can travel on a certain amount of fuel. It indicates how many miles a vehicle can cover per gallon of gas or how efficiently it uses fuel. Full definition
Used aggressively these miles can be worth significantly more, as mileage requirements for awards bookings typically do not scale in the way prices do for fares. (valuepenguin.com)
The «inflation» argument to justify increased mileage requirements is rather silly. (travelskills.com)
So I don't think there's a way to get around the higher mileage requirements by adding a partner by calling in. (uponarriving.com)