Travelers with Delta SkyMiles credit cards can earn double miles on all Delta Air Lines and Northwest Airlines flights through December 31.

Travelers with Delta SkyMiles credit cards can earn double miles on all Delta Air Lines and Northwest Airlines flights through December 31.

To qualify, new and existing cardmembers have to register at deltadoublemiles.com on or before September 30. They can then fly any Delta or Northwest flight on or before December 31 to earn double flown miles.

Qualified members are not required to purchase their ticket with a Delta SkyMiles credit card to be eligible for the bonus; and all flown travel through December 31, including previously booked travel, will earn double miles.

New customers interested in getting a Delta SkyMiles credit card can register for the promotion at deltadoublemiles.com and then apply for the card. The offer is open only to new and existing Basic Delta SkyMiles credit card members from American Express who register by September 30.

The WorldPerks/SkyMiles account registered for the promotion and associated with the primary Delta SkyMiles credit card account is the only account eligible to earn double bonus miles.