FORT WORTH, Texas — It will soon cost you $50 to upgrade from economy coach on U.S. trips aboard American Airlines.

American, which invented the mileage program 25 years ago, has notified customers it will raise fees and miles needed for upgrades and free trips.

Under changes that take effect Oct. 1, an upgrade from economy coach on a one-way domestic flight will cost $50, plus the previously required 15,000 miles. A roundtrip upgrade would be $100 and 30,000 miles.

Fees for upgrades were also raised on international flights, and some mileage requirements for earning roundtrip tickets were also boosted.

The airline told members of its AAdvantage frequent-flier program of the changes in an e-mail message.

American's moves follow changes at Delta Air Lines Inc.'s mileage program last week.

Airlines are raising fares and a variety of fees to cover higher jet fuel costs, but most U.S. carriers are still losing money. American parent AMR Corp. lost nearly $1.8 billion in the first six months of this year after earning profits in 2006 and 2007.

American also boosted the number of miles needed to upgrade full-fare coach seats to business- or first-class on some routes.

On flights to Hawai'i, Mexico or the Caribbean, it'll take 8,000 miles instead of 5,000, and Europe will be 15,000 miles, up from 10,000.

American's AAdvantage program was revolutionary when it was introduced in the 1980s, and it is often credited with helping build loyalty to the carrier.

Could more changes be on the way for frequent fliers?

In a footnote to the e-mail sent to customers, American said it reserves the right to change the frequent-flier program rules at any time, without notice.