AirTran Airways plans to start charging customers $10 — or $20 a round trip — if they check a second bag.

Citing the need to offset rising fuel costs, the Orlando-based discount carrier said it will roll out the new fee May 15.

AirTran said there still won't be an extra charge for the first checked bag, and customers can still take a carry-on bag for free. The airline is also exempting business-class passengers and customers who have reached elite status in its frequent-flier program.

Until recently, passengers on most airlines could check two bags as part of the price of the ticket. But Delta and most other big network carriers recently announced extra fees in the face of soaring fuel costs. Delta plans to charge $50 round-trip for checking a second bag starting May 1.

Delta also is adding or increasing several other fees, including a new $3-per-bag fee for check-ins at the curb that took effect this month.

The cost of jet fuel has nearly doubled so far this year, to $3.38 a gallon.

Ken Bernhardt, a professor of marketing at Georgia State University, said such fees are probably here to stay because they could do two things: generate revenue with little extra cost, and reduce airlines' fuel and labor costs, if customers bring fewer pieces of luggage.

He said customers probably recognize the fees as necessary to offset the high fuel costs airlines are facing.

"It's virtually impossible for any airline to generate profits with oil prices in excess of $100," he said.