Southwest Airlines Co, (LUV) the largest low-cost carrier, said Wednesday it soon would assign passengers a place within their assigned boarding groups but would retain its 36-year-old open seating process, which is sometimes referred to as a "cattle call."

The no-frills carrier said the plan cuts the time passengers wait in boarding lines, assigning them a numerical slot, but allows them to sit where they like on the plane, Southwest said in a statement.

Southwest, which is also beefing up its effort to appeal to business travelers, has been experimenting with alternatives to open seating for over a year. The airline said customers often line up at the departure gate 30 minutes before a flight to get a good seat.

The No. 6 U.S. airline, which is often credited with inventing the low-cost airline model, has gotten off to a slow start this year, buffeted by tougher competition, higher fuel costs, and softening demand for air travel.

Southwest hopes to increase annual revenue by more than $1 billion by 2010.

Shares of Southwest were up 13 cents at $15.20 on the New York Stock Exchange in afternoon trade.