on Delta and participating airlines, membership in our Sky Club and other program awards.  

 

Passenger Ticket Sales Earning Mileage Credits. Passenger ticket sales earning mileage credits under our SkyMiles Program provide customers with two deliverables: (1) mileage credits earned and (2) air transportation. Effective January 1, 2011, we began applying the provisions of Revenue Arrangements with Multiple Deliverables ("ASU 2009-13") to passenger tickets earning mileage credits. Under ASU 2009-13, we value each deliverable on a standalone basis. Our estimate of the standalone selling price of a mileage credit is based on an analysis of our sales of mileage credits to other airlines and customers and is re-evaluated at least annually. We use established ticket prices to determine the standalone selling price of air transportation. We allocate the total amount collected from passenger ticket sales between the deliverables based on their relative selling prices.  

 

We defer revenue from the mileage credit component of passenger ticket sales and recognize it as passenger revenue when miles are redeemed and services are provided. We record the portion of the passenger ticket sales for air transportation in air traffic liability and recognize these amounts in passenger revenue when we provide transportation or when the ticket expires unused. The adoption of ASU 2009-13 did not have a material impact on the timing of revenue recognition or its classification with regard to passenger tickets earning mileage credits. A hypothetical 10% increase in our estimate of the standalone selling price of a mileage credit would decrease passenger revenue by approximately $50 million, as a result of an increase in the amount of revenue deferred from the mileage component of passenger ticket sales.  

 

Prior to the adoption of ASU 2009-13, we used the residual method for revenue recognition. Under the residual method, we determined the fair value of the mileage credit component based on prices at which we sold mileage credits to other airlines and then considered the remainder of the amount collected to be the air transportation deliverable.  

 

Sale of Mileage Credits. Customers may earn mileage credits through participating companies such as credit card companies, hotels and car rental agencies with which we have marketing agreements to sell mileage credits. Our contracts to sell mileage credits under these marketing agreements have two deliverables: (1) the mileage credits redeemable for future travel and (2) the marketing component.  

 

ASU 2009-13 does not apply to contracts to sell mileage credits entered into prior to January 1, 2011 unless those contracts are materially modified. As of December 31, 2011, we had not materially modified any of our significant agreements. Our most significant contract to sell mileage credits relates to our co-brand credit card relationship with American Express. For additional information about this relationship, see Note 6. For contracts entered into prior to January 1, 2011 that have not been materially modified since January 1, 2011, we continue to use the residual method for revenue recognition and value only