We fly on Airtran all the time, and I pay the fee to choose a seat in advance. It has been my experience over the years, on a variety of airlines, that the airline makes no effort at all to keep parties together, even if they are on the same reservation. In particular, I remember one specific flight with my infant son that they separated my family, and we had to swap around on the plane to get a parent sitting next to the baby. But that was ATA, and at the time, everybody was assigned a seat at the airport. No choosing ahead. I think it is done by computer. My most recent trip on airtran, as a matter of fact, I chose seats when I purchased tickets in December for a March flight. I checked my reservation in February, and found that somehow, the computer had assigned somebody else to the seats I had chosen, so, I had to chose different ones. Not sure how they do that. When I originally chose the seats, the plane was close to empty. But, I got the same seat positions in a different row, so, I was OK. But, Airtran, in particular, sometimes changes plane types from the 2-3 configuration to a 3-3 configuration, which means that if they did so, there would be a whole bunch of middle seats left over, after those who had thought they were sitting next to each other on the 2 seat side of the plane (this happened to my son and me when we flew from IN to MCO in Dec 2011).