I have successfully gotten seats being on standby for many flights, both earlier and later on the ticketed day. Never a charge to do so either. I wouldn't recommend it for a Fri eve flight out of a hub though.

I don't fly CO enough to make definitive conclusions. However, they're standby rules may be more stringent, in my experience. Last year, during Memorial Day Saturday, I overheard someone who missed the plane that had to cough up $75. On the other hand, last month, I missed a flight (1 time in years) by 5-10 min. The CO agent put me on a different airline (US, not NW) even though I had a discount ticket. I consider this very courteous treatment by an airline.

travellight, I'm glad everything worked well for you, but in actuality, it was probably US you have to thank and not CO. US has been in really bad shape for several months now and in last minute situations such as yours, they'll basically take anyone's ticket, no matter what the fare paid. You said you had a discounted ticket. Well, if your ticket was non-discounted, likely any airline would take it. Depending on the circumstances, it could have been cheaper for CO to sign your ticket over to another carrier than to let you standby for the next flight.

1. Indeed, the CO computer system will cancel your downline remaining itinerary if you no-show any flight. The only way to avoid this is for an agent to cancel the flight out of your pnr that you are going to miss. The phone agents are relucant to do that, airport agents more likely to do it. I only remember a phone agent doing it for me once.

2. Once your res is cancelled, the agent (phone or airport) must rebook your entire record. If it is an e-ticket, they must re-sync your e-ticket as well. If your return flight is full in the class of service you are booked in, they can just put you in aother class. For example, they can book you in Y instead of Q. They also have a computer entry that allows them to overbook a flight in any class if they want too/feel like/your situation warrants it. They can also call a department inside CO called CRC that will allow them to overbook the flight even if it is already booked to authorization. So you would say "call crc to have it overbooked, please." If they are having trouble with your e-ticket, they can call the ATO help desk. However, the ATO help desk does not encourage waivers.

3. The two hour rule is entirely up to the discretion of the ticket counter, gate, or p-club agent. I have gone in with tickets a year old, and they have rebooked me for free. Other times, they have insisted on charging me $75 to just change one day.

4. Anne, as someone posted, technically you cannot stand-by on a flight on a different date. However, if it is at all convenient, I would encourage you to go to the airport and try your luck. They may just let you go with no charge, they may charge you $75, anything is possible. Above all, do not call and ask reservations, as they might put a note in your pnr saying "pax adv no standby allowed on different days then ticket is issued for." You don't want such a note! I have bought those 4th of July specials, and have used them on different dates. Usually they just waive it, or charge $50 saying "we really shouldn't let you fly at all, but because we are nice, we are just going to charge you the fee." It doesn't work all the time though. I have had them tell me "just pay the Y fare," and I say "I never heard you had to pay that much," and they say "sorry." So, again, anything is both possible and probable. It just depends on the agents mood, the environment in the station, and whether they like you. How arbitrary life is?