MSP-MCI was oversold by 3, a few days before christmas. $500 offer. Next flight was 4 hours later.
On the later flight, they might have done something to give me upgrade priority - I was pretty far down the list on my initial flight but was
#2 and got an upgrade on the rebooked flight
On the flight I ultimately took, they initially thought they were oversold and offered $600 for a later MSP-MSI flight, some 6 hours later. They ended up not needing anyone.