I believe DoT only mandates involuntary denied boarding compensation. Basically when you and an airline enter into an agreement for transportation between two points, the airline has the legal obligation to get you there, and if they deny you involuntarily they must pay you the compensation mandated by DoT. I would compare volunteering to settling a lawsuit out of court. If the defendant and plaintiff agree on terms and settle, the legal system has no say as to what those terms should be. If you and the airline agree on a price(which the DoT should have no say in), you give up your seat and the airline doesn't have to report an IDB to the DoT(I think they still report VDB, but not sure). I don't know if there is any year-end penalty for an airlines number of IDBs, but it is bad PR to be on the top of the list, so I would think paying a volunteer more than what they'd be obligated to pay an IDB would be better for an airline($600 should be "cheaper" than $400+ an IDB to report).

This particular idea of DLs is great for them(as long as the negative press isn't too bad), good for some consumers, and maybe not so good for some of us. For DL, if $600 is cheaper than $400+an IDB, then $200 is WAY cheaper than $400+an IDB(I'm sure this will add up A LOT over a year). Also the gate should be a little more organized if the agent has this list available to them. For the consumer that volunteers this is a great way to get their attention. I'd assume the "bid" placed at the kiosk wouldn't be binding, and the pax could opt out of it upon hearing their reroute options. For some travelers and especially for nonrevs, I think this could be bad because as each denied boarding becomes cheaper, I think flights will be oversold by more and more. I haven't seen the DoT stats in quite a while, but I believe in DBs and/or IDBs, ASA, Comair, and Delta were the worst 3 for the past few years.

This will save them a ton of money, but hopefully they don't go overboard w/ the oversales as a result.