In 1991, Delta acquired most of the assets of
Pan Am Airways, and in November 1991 all members of the Pan Am frequent flyer program, WorldPass, were transferred to Delta's FF program, with their accumulated miles. On July 31, 2008, Delta adjusted the cost of award tickets by implementing a four-tiered pricing system. For example, a domestic coach ticket cost 25,000, 32,500, 40,000, or 60,000 miles depending on availability. On July 27, 2009, Delta introduced "Rollover" for Delta Medallion members. Flyers who reach an elite tier in a program year are able to roll over any extra Medallion Qualification Miles (MQMs) above their earned tier to the next year. For example, a passenger who earned 65,000 MQM in 2010 will earn Gold Medallion status for reaching 50,000 MQMs and will begin 2011 with 15,000 MQMs rolled over from the previous year. On October 1, 2009, Northwest Airlines' former frequent flyer program, WorldPerks, officially became SkyMiles. This remained until the reservation system and website became Delta on January 31, 2010. In January 2011, Delta eliminated its mileage expiration policy, making it at the time the only major U.S. carrier to have a non-expiring mileage policy. The announcement was made on 15 February 2011. (
United Airlines matched their policy by 2019.) In January 2013, Delta announced that beginning in the 2014 program year qualifying for elite Medallion status will require meeting spending thresholds. Each tier of elite status will now require a certain amount of Medallion Qualification Dollars (MQDs), in addition to the existing mileage or segment requirements. 1 MQD is earned for every dollar spent on most Delta issued airline tickets and on Delta marketed flights on other tickets. Only the base fare and carrier imposed fees earn MQDs. Government fees and taxes, as well as ancillary services such as baggage fees, change fees, etc., do not earn MQDs. Medallion members who spend at least $25,000 on a cobranded Delta
American Express card annually are exempt from this new requirement. On September 26, 2017 Delta announced that the Credit Card waiver for Diamond Medallions only, was being increased to $250,000 which effectively eliminates it for many travelers. In late February 2014 Delta announced significant changes to the SkyMiles program that shifts away from miles traveled to earning based on Medallion level and dollars spent, ceasing to be a frequent flyer program and becoming a spending program. Also announced was a new mileage redemption structure that will approve Award seat availability. The minimum number of miles earned per dollar is 5 and the maximum per dollar is 13. SkyMiles members that use one of Delta's branded credit cards from American Express will receive a bonus of 2-3 additional miles per dollar spent with Delta, depending on the tier of card used. It was also announced that the maximum number of miles that can be earned on any ticket is 75,000. The updates to the 2015 SkyMiles program will not impact how one earns different Medallion levels from the 2014 MQD scheme. Partnerships with
Airbnb have also been announced. ==COVID-19 pandemic effect==