To participate in this public offer, customers must be a new or existing SkyMiles member and must first register online and book by Dec. 31, 2013 (ending 11:59:59 PM, U.S. CDT on 12/31/13), and fly between Oct. 18, 2013, and Oct. 31, 2014. This offer is nontransferable. Promotional registration is required before purchasing and taking flight, and only tickets purchased (following promotional registration) will qualify for this bonus.Customers must book by Dec. 31, 2013, then fly on Delta or Delta Connection-marketed and -operated flights to or from Seattle and the following cities: Anchorage, Alaska, Las Vegas, Los Angeles, Portland, Ore., San Diego, and San Francisco between Oct. 18, 2013, and Oct. 31, 2014, and earn double bonus miles and double Medallion® Qualification Miles (MQMs) on all flight segments purchased with a published fare that earns full mileage accrual. There is no limit to the bonus miles and MQMs that can be earned within the qualification period. Travel may originate or terminate in any city; however, bonus miles and MQMs will only be earned based on travel flown on Delta-operated flights to or from Seattle and the eligible cities listed. Codeshare flights operated by carriers other than Delta or Delta Connection are excluded from this offer. Qualification Miles (MQMs) are used for Medallion status qualification and are based on calendar year activity. Starting January 1, 2014, Medallion status for U.S.-based members will be earned with MQMs or Medallion Qualification Segments (MQSs) plus a new threshold – your annual spending on Delta flights, which will be measured by Medallion Qualification Dollars (MQDs). You may visit delta.com/mqds for more details on Medallion qualification. Travel must be between Oct. 18, 2013, and Oct. 31, 2014. All travel must be completed by Oct. 31, 2014.