NEW YORK (CNN/Money) - In peace times, passengers must pay as much as $100 to change their travel itineraries. But now that conflict with Iraq has begun, major airlines are waiving such fees for passengers who want to postpone their travel plans.

The details of these war-related cancellation policies vary from one airline to the next. In general, passengers can delay their trips until the end of the year, without penalty, as long as changes are made within 30 days and before the original travel date.

Keep in mind, however, that in most cases the full value of your ticket will be applied to the price of a new ticket. If the price of your new ticket is higher, you'll have to pay the difference.

Below are some details of the largest airlines' relaxed policies, as of March 20. Southwest has not made any changes to its cancellation policy because, unlike the other carriers, it does not charge a fee for rebooking tickets.

Alaska/Horizon: Passengers traveling between March 19 and May 18 have until April 19 to rebook their flights without penalty. Rescheduled travel with the airline must be completed by Dec. 31.

American: Tickets purchased anytime through April 19, for travel through May 18, can be changed without penalty as long as changes are made by April 19 and before the original flight date. Travel can be postponed until Dec. 31. American's policy, as with many other carriers, also applies to passengers who have already traveled to their destination and want to return early.

Continental: Domestic passengers with tickets issued on or before March 19 who are scheduled to fly through May 18 may postpone their trips until Dec. 31. Changes must be made by April 19 or the original travel date. Continental's policy also applies to international passengers who purchase tickets through March 31, as long as they change their ticket before May 31 or the original travel date.

Delta: Customers with tickets issued on or before March 19 may rebook their travel for another time and destination without penalty. New plans must be made by May 31, and domestic passengers must embark on the outgoing leg of their trip by that date. International travelers on Delta may postpone their departure through Dec. 31.

Northwest: Passengers with tickets issued on or before March 19 and scheduled to fly through May 19 can postpone their trip through Dec. 15 without penalty. This policy applies for travel within North America and the Caribbean. International passengers scheduled to fly Northwest/KLM through June 19 may postpone through Dec. 15. All changes must be made by April 19.

United: Customers with tickets issued on or before March 31, with travel dates on or before May 18, may postpone their travel, with all legs of the trip completed by Dec. 31, without penalty. Here again, United passengers must change their itinerary by April 19 or before the original travel date.

US Airways: Customers can make changes to itineraries for travel originating March 19 through June 17 without incurring standard change fees. Domestic flights or flights to Canada may be postponed through June 17. International trips can be postponed through Dec. 15. US Airways' policy applies to tickets purchased, and award tickets issued, on or before April 2. Itinerary changes must be made prior to the scheduled departure or before April 2.