Southwest Airlines (LUV) said Tuesday that it flew more passengers in May compared with the year-earlier period, helped by its recent AirTran buy.

The airline, which acquired AirTran Airways for $1.14 billion last month, said it flew a combined 9.2 billion revenue passenger miles, up 10.6% compared with 8.3 billion a year ago. The company said it combined results from both companies for comparative reasons. 

The Dallas-based company said available seat miles were up 4.2% to $11.1 billion from $10.7 billion in the same month in 2010. Load factor was also improved, up to 82.7% from 77.9% last year.

Excluding AirTran, Southwest said passenger revenue per available seat miles climbed in the 11% to 12% range.

While high oil costs have forced many airlines such as Delta (LUV) to slash production, Southwest said it flew 121,302 flights in May, up 2.3% from 118,612 flights last year.

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