There are some airlines that do not set out to oversell/overbook flights - JetBlue, for example. Even in a situation where a flight is only sold to capacity, th

There are some airlines that do not set out to oversell/overbook flights - JetBlue, for example. Even in a situation where a flight is only sold to capacity, there can be various reasons for people to be IDBed. Damaged seats, Equipment Changes (A321 -> A320 for example), etc. At some point, every US carrier has has or will have to IDB people, and they all have a policy that gives them as much leeway as possible under federal regulations to do so.