45 A321-200, 25 A330-900neo, 25 A350-900, 19 E190-100, 18 B-787-8 and six A330-300 aircraft. Our purchase commitment for the 18 B-787-8 aircraft provides for certain aircraft substitution rights, including for our current orders of B-737-900ER aircraft.

Contract Carrier Obligations. Represents our estimated minimum fixed obligations under capacity purchase agreements with third-party regional carriers. The reported amounts are based on (1) the required minimum levels of flying by our contract carriers under the applicable agreements and (2) assumptions regarding the costs associated with such minimum levels of flying.

Employee Benefit Obligations. Represents primarily (1) our estimated minimum required funding for our qualified defined benefit pension plans based on actuarially determined estimates and (2) projected future benefit payments from our unfunded postretirement and postemployment plans. For additional information about our employee benefit obligations, see “Critical Accounting Policies and Estimates.”

Other Obligations. Represents estimated purchase obligations under which we are required to make minimum payments for goods and services, including, but not limited to, insurance, 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 the Notes to the Consolidated Financial Statements.

Frequent Flyer Program

Our SkyMiles Program offers incentives to travel on Delta. This program allows customers to earn mileage credits by flying on Delta, Delta Connection and airlines that participate in the SkyMiles Program, as well as through participating companies such as credit card companies, hotels and car rental agencies. We sell mileage credits to non-airline businesses, customers and other airlines. Effective January 1, 2015, the SkyMiles program was modified from a model in which customers earn redeemable mileage credits based on distance traveled to a model based on ticket price. This award change did not affect the way we account for the program.

The SkyMiles Program includes two types of transactions that are considered revenue arrangements with multiple deliverables. As discussed below, these are (1) passenger ticket sales earning mileage credits and (2) the sale of mileage credits to participating companies with which we have marketing agreements. Mileage credits are a separate unit of accounting as they can be redeemed by customers in future periods for air travel 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. We value each deliverable on a standalone basis. Our estimate of the selling price of a mileage credit is based on an analysis of