our commitments to purchase 18 B-787-8 aircraft and 12 previously owned MD-90 aircraft. The table excludes our orders for five A319-100 aircraft and two A320-200 aircraft because we have the right to cancel these orders. For additional information, see Note 7 of the Notes to the Consolidated Financial Statements.  

      Other Obligations. Represents primarily estimated purchase obligations under which we are required to make minimum payments for goods and services, including but not limited to insurance, outsourced human resource services, marketing, maintenance, technology, sponsorships and other third party services and products.  

Critical Accounting Policies and Estimates  

     Our critical accounting policies and estimates are those that require significant judgments and estimates. Accordingly, the actual results may differ materially from these estimates. For a discussion of these and other accounting policies, see Note 1 of our Notes to our Consolidated Financial Statements.  

Frequent Flyer Program  

     Our frequent flyer program (the “SkyMiles Program”) offers incentives to increase travel on Delta. This program allows customers to earn mileage credits by flying on Delta, regional air carriers with which we have contract carrier agreements (“Contract Carriers”) and participating airlines, as well as through participating companies such as credit card companies, hotels and car rental agencies. We also sell mileage credits to non-airline businesses, customers and other airlines. Mileage credits can be redeemed for air travel on Delta and participating airlines, membership in our Sky Club and other program awards.  

     We use the residual method for revenue recognition of mileage credits. The fair value of the mileage credit component is determined based on prices at which we sold mileage credits to other airlines, $0.0054 per mile at December 31, 2010, and is re-evaluated at least annually. Under the residual method, the portion of the revenue from the sale of mileage credits and the mileage component of passenger ticket sales that approximates fair value is deferred and recognized as passenger revenue when miles are redeemed and services are provided. The portion of the revenue received in excess of the fair value of mileage credits sold is recognized in income when the related marketing services are provided and classified as other revenue. For additional information, see “Recent Accounting Standards.”  

     For mileage credits which we estimate are not likely to be redeemed (“Breakage”), we recognize the associated value proportionally during the period in which the remaining mileage credits are expected to be redeemed. The estimate of Breakage is based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have a material impact on our revenue in the year in which the change occurs and in future years. At December 31, 2010, the aggregate deferred revenue balance associated with the SkyMiles Program was $4.5 billion.