If you've struggled to redeem your miles for flights on Atlanta's biggest airlines, you're not imagining things.

Delta Air Lines again came in near the bottom of a ranking on the availability of certain mileage award seats, ahead of only US Airways, according to a new study. The top-ranked U.S. carrier: Southwest Airlines, which will enter the Atlanta market through a buyout of AirTran Airways that closed earlier this month.

According to the study released by consulting firm IdeaWorks on Thursday, searches for the award seats at the lowest 25,000 mile level on Delta were successful 27.1 percent of the time -- which was still nearly twice the availability on Delta in the study last year, the first time it was conducted.

"We're pleased with that progress and we'll continue to listen to customer feedback," Delta spokeswoman Chris Kelly Singley said.

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Meanwhile, on Southwest, award seats were available 99.3 percent of the time using its "anytime" or "wanna get away" awards.

AirTran ranked No.21, with 47.1 percent availability. Southwest expects to fold AirTran passengers into the Southwest frequent flier program as it combines the two carriers' operations in the next couple of years.

The study was based on queries made in March and April for seats on 20 popular routes on each airline for June through October. This year, IdeaWorks did a separate test with queries for award flights on short notice, which yielded many more award seats on Delta, at 42.5 percent availability.

That suggests travelers may find more seats available within three weeks of the flight. Singley said one of the ways Delta has increased award availability is offering seats close to the date of departure that the airline doesn't expect to sell.