Originally Posted by Tom Williams
Just to clarify the terminology - I understood that a flight is overbooked when they have confirmed reservations for more passengers than there are seats on the plane. The flight is not oversold until enough confirmed passengers show up at the gate that they actually have to turn someone away either through VDB or IDB.
I think this is unique to Delta, there is no broader industry wide differentiation like this between the terms overbooked/oversold at many carriers, but this post here from a waaays back has some more detail on the differences:
Overbooked vs. Oversold? and question on overnight bumps in ATL
Each flight has an overbooking profile. At your typical major carrier, revenue management uses (usually quite sophisticated) modelling software that analyses historical patterns and the level of no-shows or last minute cancellations for that flight. There can be marked differences in overbooking for flights departing out of a hub (potential for misconnects) versus the inbound spoke departing from an outstation going in TO a hub (no misconnects).
There's also regional variations and anomalies on International routes. Flights in and out of India are frequently oversold by as much as 100 on a widebody aircraft from say DEL-LHR.
Some carriers are definitely better than others at managing the overbooking profiles. For instance, some carriers will manually over-ride the overbooking profile during Thanksgiving or Christmas when there's a high percentage of leisure travel, not many no-shows, and where there's very little "slack" to re-accommodate displaced passengers from misconnects or cancelled flights etc.
Also, some carriers have a "no overbook policy" for premium cabins and only oversell the main/Y cabin, yet others like UA will often overbook the J cabin on Japan flights by up to 6 seats.
There are also the occasional rare "holy grail" flights that seem to somehow slip through the computer modelling, and are consistently overbooked and consistently need VDB's. I remember a BD flight in the UK from LHR-DUB on a Friday around 7pm which was always
oversold, and I actually knew people who'd regularly book several weekend trips to DUB when seat sales were being offered, knowing that they'd get the option to VDB on as many as 2/3rds of those flights and make out handsomely.