Frequent fliers on American Airlines Inc. got hit with another round of fees on Thursday – this time to upgrade discounted economy class tickets to the business and first class cabin.

Such one-way upgrades for trips in North America and between North America and Central America will cost customers $50, plus 15,000 frequent flier miles, starting Oct. 1.

And fees to upgrade a discounted economy seat on flights between North America and certain parts of South America, Asia and Europe will jump from $300 to $350 one way.

The fees signal a second round of changes for the Fort Worth-based carrier's AAdvantage program, and the latest attempt by the airline to boost revenue in the face of skyrocketing fuel prices.

The AAdvantage fees announced Thursday were driven by higher fuel costs and rising airfares, said Marcy Letourneau, an American spokeswoman.

"The disparity between discount and premium tickets is too great to be offset by miles alone," she said.

In May, the airline announced higher mileage requirements for most trips starting in October. And in June, it implemented a $5 booking fee for award tickets that officials said would help pay for recent technology.

American's new fees are similar to ones charged by some other frequent-flier programs, said Randy Petersen, publisher of InsiderFlyer magazine.

In recent months, American has also rolled out new fees for checking bags and raised charges for unaccompanied minors, overweight bags and traveling with pets.

Across the airline industry, carriers are increasingly charging for services and amenities once included in a ticket in an effort to raise revenue.

On Tuesday, Delta Air Lines Inc. began charging $50 for a second checked bag – twice the fee charged by several of its peers.

JetBlue Airways Corp. said Monday that it would begin selling pillow-and-blanket kits for $7.

And last week, US Airways began charging for soft drinks.

Timothy Sieber, an aviation consultant for the Boyd Group in Evergreen Colo., said the high fuel costs are to blame for the new fees, which may be reaching a tipping point.

"At some point, it becomes like a Saturday Night Live skit, where you're paying for a seat belt and to use the bathroom," Mr. Sieber said. "They're running out of things to charge us for."

During the last seven years, U.S. carriers have looked into every nook and cranny to find savings, only to have fuel rise to record levels. Fuel once represented 20 percent to 25 percent of an airline's costs but has grown to 40 percent.

"That's a huge hole to fill," Mr. Sieber said.

Even so, some of the recently announced fees might end up being short-lived if they aren't widely adopted by industry players.

The $15 fee adopted by American and others for the first checked bag, for example, hasn't been echoed by Delta. And Dallas-based Southwest Airlines Co. still offers two checked bags for free, a point that it has been emphasizing in a recent ad campaign.

"We'll see what, if any, of these amenities come back because of competitive reasons," Mr. Sieber said.