Delta Air Lines issues travel vouchers, which you can redeem like cash for travel with the carrier, for many reasons. These reasons include service disruptions--if, for example, your flight is oversold and the gate agent asks you to stand by for a later flight--and ticket cancellations. No matter the reason Delta issued you the voucher, it expires one year from that date. While the airline does not officially extend vouchers, there is a loop hole you can employ to allow yourself more time to travel.
Make a reservation with your voucher by calling Delta reservations at 1-800-221-1212 for domestic U.S. flights or 1-800-241-4141 for international flights. Make sure you book yourself to travel before the expiration date of your voucher. For example, if your voucher is set to expire on February 19, 2011, you shouldn't attempt to book travel on March 1, 2011.
Cancel your reservation before your date of travel to receive a new voucher from Delta. Point your browser to the link listed in "Resources" and click your mouse in the circle next to "eTicket Number." Enter the first and last name as printed on the ticket and the ticket number, then click "Search." Click "Edit Itineraries," then the "Cancel Itinerary" button next to yours. Wait for an email from Delta containing details about your new travel voucher, which will expire one year from the date you cancel your reservation.
Call Delta reservations to book travel with your new voucher, keeping in mind that you must complete travel by the expiration date of your new voucher.