United Continental Holdings had the highest balance of outstanding debt among enhanced equipment trust certificate (EETC) issuers through 28 March 2013, according to Jefferies' fixed income research.
Global airlines had $21.9 billion in outstanding EETC obligations, and non-North American-based airlines accounted for $735 million of that amount.
The Chicago-based carrier amassed $8.2 billion in outstanding EETC debt, based on 25 separate transactions issued between 1997 and 2012.
Delta Air Lines finished a distant second with a balance of $4.5 billion on the back of 13 transactions.
US Airways issued 13 EETC deals between 1998 and 2012 and had $3.3 billion in outstanding debt. Not included in the total is the carrier's $819.6 million EETC, which came to market this month to finance 18 Airbus aircraft.
American Airlines' outstanding EETC balance totalled $2.7 billion due to eight transactions issued from 2001 through March 2013. Its latest offering, a $663 million private placement, marked the first EETC issued by a carrier in Chapter 11 bankruptcy protection.
Freighter operator FedEx has tapped the market three times, resulting in an outstanding debt balance of $902 million at 31 March. The carrier's most recent offering involved a $250 million EETC financing due in 2018.
JetBlue and Emirates had similar levels of EETC debt - $583 and $588 million, respectively. Emirates' Doric Nimrod Air Two transaction became the fist non-US EETC to come to market since the financial crisis of 2008. The transaction financed four Airbus A380s in June 2012.
Southwest Airlines and Atlas Air also accumulated almost identical EETC debt levels of $456 million and $455 million, respectively, while Iberia had an outstanding balance of $147 million.