Statements.

Financial Condition and Liquidity

We expect to meet our cash needs for the next 12 months from cash flows from operations, cash and cash equivalents, short-term investments and financing arrangements. As of December 31, 2015 , we had $5.6 billion in unrestricted liquidity, consisting of $3.4 billion in cash and cash equivalents and short-term investments and $2.2 billion in undrawn revolving credit facilities. During 2015 , we generated $7.9 billion in cash from operating activities, which we used to fund capital expenditures of $2.9 billion , return $2.6 billion to shareholders, reduce the principal on our debt and capital lease obligations by $1.5 billion and fund equity investments of $500 million , while maintaining a solid liquidity position. Sources of Liquidity

Operating Activities

Cash flows from operating activities continue to provide our primary source of liquidity. We generated positive cash flows from operations of $7.9 billion in 2015 , $4.9 billion in 2014 and $4.5 billion in 2013 . We also expect to generate positive cash flows from operations in 2016 .

Our operating cash flows can be impacted by the following factors:

Seasonality of Advance Ticket Sales . We sell tickets for air travel in advance of the customer's travel date. When we receive a cash payment at the time of sale, we record the cash received on advance sales as deferred revenue in air traffic liability. The air traffic liability increases during the winter and spring as advanced ticket sales grow prior to the summer peak travel season and decreases during the summer and fall months.

Fuel and Fuel Hedge Margins . Including our regional carriers, fuel expense represented 23.0% of our total operating expenses for 2015 . The market price for jet fuel is highly volatile, which can impact the comparability of our cash flows from operations from period to period.

As part of our fuel hedging program, we may be required to post margin to counterparties when our portfolio is in a loss position. Conversely, if our portfolio with counterparties is in a gain position, we may receive margin. Our future cash flows are impacted by the nature of our derivative contracts and the market price of the commodities underlying those derivative contracts. Our hedge contracts were in a net loss position at December 31, 2015 and 2014, resulting in $119 million and $925 million, respectively, of margin postings to counterparties.

Timing of SkyMiles Sales. In December 2011, we amended our American Express agreements and agreed to sell $675 million of unrestricted SkyMiles to American Express in each December from 2011 through 2014. Pursuant to the December 2011 amendment, American Express purchased $675 million of unrestricted SkyMiles in each of those years with the final payment in 2014. The SkyMiles purchased in December 2014 were utilized by American Express in 2015. There were no advanced sales of SkyMiles in 2015.

Pension Contributions. We sponsor defined benefit pension plans for eligible employees and retirees. These plans are closed to new entrants and are frozen for future benefit accruals. Our funding obligations for these plans are governed by the Employee