by Matt Alderton | July 22, 2015
Delta Air Lines is dramatically overhauling its SkyMiles frequent flier program, it announced this week: Next summer it will become the first "Big Three" U.S. airline to abandon its fixed-miles system for one that's based on supply-and-demand.

"We know your miles are important, so we want to provide the most notice possible regarding award price changes," Delta reported. "For travel on or after June 1, 2016, the number of miles needed will change based on destination, demand, and other considerations."

This means that travelers who previously could book a free flight to anywhere once they'd accumulated a set number of miles will now have to accumulate more miles to travel to popular destinations -- and could have to accumulate fewer miles to travel to less popular destinations.

However: "Most award prices will remain unchanged," stressed Delta.

To counteract negative sentiment around increased mileage requirements for some destinations, Delta is making it easier to earn miles: Effective for travel starting July 21, 2015, it said, passengers who purchase Preferred Seats, Delta Comfort+, and paid upgrades to the premium cabin will now earn miles. The airline also has increased by 50 percent the number of domestic award seats available at the lowest prices, expanded to 22 the number of partner airlines with which miles can be redeemed, created new mileage-earning opportunities with car rental companies, and enabled award booking through its mobile app.

For more information about these and other changes to the SkyMiles program, read Delta's complete announcement.