(Updates to add Delta's figures.) 
   DOW JONES NEWSWIRES 
 

Southwest Airlines Co. (LUV) said its passenger traffic rose slightly in August as its plane flew with more passengers, while the low-cost carrier followed the industry trend to cut capacity.

Meanwhile, traffic at Delta Air Lines Inc.'s (DAL) Delta and Northwest operations fell 2.2%, down 1.3% domestically and 3.5% abroad. Overall, the world's largest carrier's load factor increased to 86.6% from 85.7%.

Thursday, AMR Corp.'s (AMR) American Airlines and UAL Corp.'s (UAUA) United Airlines both reported lower passenger traffic in August, although low-cost carriers like Southwest have said their business is improving.

Its traffic was up was up 1% and load factor, or the number of filled seats per plane, jumped to 80.2% from 74.6% as capacity fell 6.1%.

Passenger revenue per available seat mile, a key airline performance metric, was estimated to have dropped in the 5% to 6% range amid falling fares industrywide.

On Monday, Continental Airlines Inc. (CAL), the first major international carrier to report results, estimated August traffic slid 3.9% on a 6% reduction in seat capacity, compared with last year.

Southwest shares were up 1.3% to $8.52 in recent trading while Delta gained 2.5% to $7.34.

-By Joan E. Solsman and John Kell, Dow Jones Newswires; 212-416-2291; joan.solsman@dowjones.com