Tell the agent at check-in you want to be put on the list. Then confirm you are on the list once you get to the gate. I did this this past week and was told at the gate "we will need your seat. . ." Waited and waited - at the very last moment - they didn't need me. So just be prepared that although it may look like you will be bumped it isn't for sure until the very very end. Also, I noticed that the gate agents don't like to be "bugged" by people so just remind them when you are at the gate and then step aside (but don't miss your flight! )