As of July, passengers flying from Chicago to Detroit will no longer earn 500 miles for frequent flier credits, the Chicago Tribune reported.

By eliminating its minimum reward of 500 miles and switching to a per mile system, passengers making the Chicago to Detroit hop will receive 234 miles one way.

The minimum reward had been in place more than 25 years, the Tribune reported.

"There's a profusion of miles out there; it's like funny money," aviation consultant Robert Mann told the newspaper.

Skyrocketing jet fuel costs are forcing airlines to push back perks and add to various fees. United recently added a $25 service fee for some passengers checking a second bag, the report said.

But, an airline spokeswoman said the change in the frequent flier program was implemented to reduce the 511 billion unused miles in the carrier's Mileage Plus program.