[Note: Most of the comments in this section apply to US domestic flights
only.  US Department of Transportation rules apply only to flights
between points in the US. Airlines do not need to give any
compensation for international flights, so what, if anything, you get
for an involuntary bump is entirely up to the airline.]

Airlines tend to overbook their flights in case of no-shows. (Airlines
also ignore the overbook limit when a customer is buing a full-fare
ticket, because the cost of bribing volunteers with a bump ticket is
usually less than the additional income derived from a full-fare
ticket.)  Occasionally this will mean that more people show up with
confirmed reservations than there are seats on the plane. (Or if the
flight is a particularly full one, it may exceed the weight limit even
with empty seats.) The airline will ask if there's anyone willing to
be bumped from the flight in exchange for compensation (e.g., USAir
will give you a free round-trip ticket anywhere in North America). The
airline will then put you on the next available flight to your
destination, along with your free ticket. 

Vouchers are typically valid for only a year from date of issue. But
if you ask *before you get the ticket*, you can sometimes get it
extended for a month or two beyond the year limitation. (Some folks
have reported success in getting vouchers extended a month or so
before expiration.) If your voucher is expiring you can also try using
it to get a ticket with a particular origin and destination
but no specific departure and return dates. Such tickets should be
good for 12 months. Many bump vouchers, however, prohibit exchanging them
for such "open" tickets. An alternative is to use the voucher to book
a flight to your favorite destination for some likely dates. If the
dates don't work out, you can usually rebook the tickets for different
dates for a small fee. 

So another way to reduce the cost of flying is to volunteer to be
bumped. You can maximize your chances of being bumped by purchasing a
confirmed reservation on flights that are most likely to be full. A
good time is 7-10 am or 4-7 pm on a weekday (especially Monday morning
and Friday afternoon). These are the times most businessmen fly
(trying to make early morning meetings or to get home for dinner in
the evening), and hence when the airline is most likely to be
overbooked. Airlines are also likely to be overbooked on Sunday nights
(early evening) and the beginning and end of holidays, since that is
when non-businessmen typically fly. For example, right before
Thanksgiving and the Sunday or Monday after are prime bumping times.
The same is true of typical spring break destinations toward the end
of March and beginning of April. Receiving a free roundtrip ticket
effectively cuts your air travel costs in half.  And if you get bumped
while using a previous free bump ticket, it gets even cheaper.

Even on the best days for being bumped, the likelihood is still rather
low. Airline yield software has been getting better and better, so it
is uncommon for bumping to occur.  The DOT figures cited in [4-4]
show that American had an involuntary bump rate of 1 in 200,000 in 1993.
(These figures do NOT include voluntary bumps, which are more likely.
The DOT does not collect statistics on voluntary bumping. Note also
that American had the lowest involuntarily bump rate. The likelihood
of your being bumped voluntarily on an average carrier is probably
close to 1 in 10,000.)

If you want to be bumped and notice that the flight looks full, get to
the gate as early as possible (e.g., 1-2 hours before departure) and ask
the gate agent whether they are overbooked. If they are, they will
need volunteers. Ask them to put your name on the bump list (aka "bump
queue"). Bump tickets are offered on a first come/first served basis,
so you want to get your name near the top of the list. This will give
you priority if there are only a few bumps.  Note, however, that by
pre-volunteering, you're only likely to get a free ticket in addition
to rebooking on a flight later that day. If nobody volunteers and you
wait until they ask for volunteers, you can sometimes up the ante,
depending on how desperate they get. (Some airlines give all
volunteers the same thing, no matter when they volunteered. Others
will process you as soon as you volunteer, so the later you volunteer,
the better the incentive.) In general, you should put your name on the
bump list, and don't wait until the airline calls for volunteers.
Enough people volunteer ahead of time these days that if you don't put
your name on the list, you won't have the opportunity to be bumped
(except on very rare occasions, when not enough people volunteer).

When you get your bump ticket and are being rebooked on a later
flight, if the delay is a few hours, ask the gate agent if they can
give you a meal voucher. This voucher, which is worth $5-$10, can be
used at airport restaurants to get something to eat. Not every airline
and not every gate agent will give you one, and they certainly won't
give you one if you don't ask for it, but sometimes they will. If you
have any other special requirements (e.g., you want extra frequent
flyer credits, you want the free ticket to be good for an extra month,
etc.) it doesn't hurt to ask.

If you have a confirmed reservation, and you notice the flight is
overbooked but first class is underbooked and you don't necessarily
want to be bumped, try being the last person on line. If you are lucky
the coach and business class will be full, and they will have to
upgrade you to first class at no charge.  (Also, having a pre-issued
boarding pass will decrease your chances of an involuntary bump.) This
is risky, though, because you might wind up being bumped anyway, so
only do it if you don't care whether you'll be bumped.

It always pays to volunteer to be bumped, even if the flight isn't
overbooked. If the airline needs adjacent seating for a family, they
will sometimes bump you into first class if you are in a row by
yourself.

When you arrive at the airport, check the flight schedules to see
which flights (on the airline and its competitors) will be departing
for your destination, and when. Airlines are extremely reluctant to
book a volunteer on another carrier, so if you get bumped on the last
flight to your destination, you may have to stay overnight at a hotel.

Good days to get bumped include: Wednesday before Thanksgiving, Sunday
after; couple days before and after Christmas weekend; ditto with New Years.
Friday afternoons, evenings, and Sunday afternoons and evenings also
bump a lot.

Another trick is to ask your travel agent which flights are full or
nearly full and to purchase tickets for one of those flights. (Not
every travel agent will let you do this.) Note, however, that you
probably won't be able to get the discount rate for such a flight,
since all the seats in the discount coach fare class have probably
been sold. Also, if a flight has reached the overbook limit, you won't
be able to buy any ticket for the flight, except perhaps a full fare
ticket.

If the airline still has plenty of coach seats a day or so before the
flight, it is unlikely that they will bump.

   Here's what some airlines usually give volunteers:
      Delta, USAir:  Open roundtrip
        (Delta requires reservations three days before flight time on
        bump tickets.)

      United: Travel voucher in increments of $100 based on how long you have
      to wait for your next flight (e.g., 2 hour wait is $200), up to
      a maximum of $300. You can also ask for a food voucher.

      Continental: US domestic roundtrip ticket. Sometimes offers a
      dollar amount in credit to be used towards any Continental
      flight (e.g., $300).

      American, America West, Southwest, Northwest:  $$ off another
      ticket (usually $150 to $300; Northwest generally around $300;
      American has been known to go as high as $1000.)
      Dollar-denominated vouchers are not subject to tax, so they
      stretch further. Amounts depend on the degree of overbooking of
      the flight. United sometimes will also issue a
      dollar-denominated voucher. 

      United bumps more than average, Delta less. 

      Air Canada offers $150 cash or $300 in travel vouchers.

If you are bumped and the next flight out is the next day, the airline
may offer you overnight accomodation in addition, especially if you
are bumped while away from home.

Most bump tickets (vouchers) are non-transferable, so you must use
them yourself. If the voucher must be exchanged for a ticket,
you may be able to have the ticket issued in someone else's name,
given a reasonable excuse (e.g., your girlfriend/boyfriend).

If you are bumped (voluntarily or involuntarily) and have checked
baggage, the airline will not remove your bags from the plane. The bags
will continue on to your destination and wait there until you arrive.
So if you're planning to be bumped, bring enough clean clothes in your
carry-on to last you a day or two just in case your bags are lost or
stolen by the time you arrive, or you get stuck at a connection.

If you get bumped or your flight is canceled and need to stay at a
hotel overnight, hotels near the airport will often give you
a substantial discount if you ask for it (50% discount is not unheard
of). Ask for the "Distressed Passenger Rate". Airlines also have
overnight kits they can give you. 

A flight being cancelled is *not* the same as being bumped. Bumping
occurs only when the carrier has more passengers with confirmed
tickets on the flight than seats. You can get compensation if you are
bumped, but not if the flight is cancelled.

If airline delays cause you extra expense, the airlines may be willing
to help you out. For example, if the airline delay caused you to miss
the cheap bus shuttle service to downtown, the airline may be willing
to pay the difference between cab fare and shuttle fare. But in
general, there aren't any policies for compensation (e.g., meals, hotel,
etc.) that must be given to bumped and delayed passengers. Some
airlines are very nice and will give you food coupons if you ask, some
won't. 

Under Department of Transportation rules, an involuntarily bumped
traveler who is delayed more than one hour but less than two on a
US domestic flight is entitled to $200 or 100 percent of the one-way
fare, whichever is less (the airline must also honor the original
ticket).  For delays longer than two hours, the compensation doubles.
The calculation of delay is according to the time of arrival at the
destination.  Airlines can offer you a travel voucher (for a free
US domestic round-trip ticket) in lieu of cash, but must give you the
cash if that's what you want. Airlines like bumped volunteers because
free travel vouchers cost them less than the cash compensation they're
required to offer involuntarily bumped passengers. Approximately 1 in
10,000 passengers is bumped involuntarily. (If the involuntarily
bumped passengers are put on a flight which brings them to their
destination within an hour of the original flight time, the airline
has met its requirement.) Anything more is strictly the policy of the
airline, which is stated in its Conditions of Carriage statement. (To
obtain this statement, get it either from your travel agent or by
writing to the customer affairs office of your airline. Be sure to ask
for the full copy of the conditions; otherwise they'll give you just a
three page summary of the limitations of liability sections.) Note
that these rules do NOT apply to delayed passengers in general, just
to involuntarily bumped passengers.

According to a 1994 Supreme Court ruling, passengers who are denied
boarding can sue the airline for compensatory damages, but not punitive
damages. So in most cases you are better off accepting the
compensation offered by the airlines.

Note that if you don't show up at the gate 15 minutes before
departure, the airline can involuntarily bump you and not owe you
anything. 

There are no rules governing compensation for volunteers -- airlines
can offer as little or as much as it takes to bid you off the flight.
   Delta restricts reservations using volunteer bumped vouchers 
   to two days in advance.

Re-booking: Most volunteers are routinely booked on another flight
within a few hours, but re-routing isn't a legal requirement. Before
giving up your seat, ask when the next flight leaves, whether you'll
have a confirmed or standby reservation and (if the flight is with
another carrier) whether you'll have to pay additional fare.
Negotiating: Most airline managers can escalate compensation offers in
an attempt to get enough volunteers. So you might get a better deal by
simply asking for one. American Airlines, which has the lowest rate of
involuntary bumpees in the industry, tends to be the most generous
with compensation for volunteers.

Sometimes, when all of the airline's flights are full, they will
reroute you on another airline. However, if you are flying on a free
ticket (e.g., frequent flyer ticket, previous bump ticket), they may
not be willing to endorse your ticket over to the other airline. (It
doesn't hurt to ask.) So they'll have to send you out on another
flight later that day. If this happens and "inconveniences" you (i.e.,
you have to wait another hour or so), you may be able to weasel
something else out of the airline -- a roll of quarters for the
pinball machine, use of their club facilities, first class
accomodations on the later flight, meal voucher, or something.

If you volunteer and they don't need to bump you, you don't lose your
seat. If you volunteer, they need you, and you change your mind, you
may lose your seat, and wind up in a random seat. That is, of course,
if the airline decides to accommodate you. Once you've volunteered and
they've accepted your offer, you can't really reneg on it.

If you are bumped on an international flight, the airline will reroute
you but generally not offer you any extra compensation. Involuntary
reroutings may involve upgrading your class of service (at no extra
cost to you) or putting you on a different carrier to your destination
at the same or higher class of service. If rerouting you requires an
overnight stay, the airline will provide you with vouchers for hotel
rooms and meals. But you won't get any free tickets, and writing a
letter of complaint to the airline probably won't get you anything.
(The only case where complaining will get you something is if you paid
for a first class ticket, and they rerouted you on a lower class of
service. If this occurs, ask the airline to refund the difference in
fares.) If you're traveling international and don't want to be bumped,
buy a first class ticket. Airlines rarely bump first class passengers.