Delta and Northwest, hobbled by high fuel costs and heavy debt and pension obligations, filed for bankruptcy protection from creditors yesterday - becoming the third and fourth major carriers to enter Chapter 11 since the 2001 terrorists attacks.
Delta's late-afternoon filing included its low-fare carrier Song and was followed shortly afterwords by Northwest.
Delta's total debt is roughly $28.3 billion, and it listed $21.6 billion in assets, according to the filing.
The asset figure would make Delta's bankruptcy the ninth-largest in U.S. history, according to bankruptcy tracker New Generation Research.
Delta and Northwest said passengers were not expected to see any immediate effects from the filing.
Delta also promised to honor all tickets and sent a letter to frequent-flier customers seeking to reassure them, reports New York Daily.
Three of the U.S.'s four largest airlines are now operating in bankruptcy. United, the second-largest carrier has been in Chapter 11 for almost three years.
With US Airways also in bankruptcy, there are now four carriers in Chapter 11, representing nearly half of the nation's airline capacity, according to an analysis by the financial firm Bear Stearns.
Delta has been struggling for more than a year to stay out of bankruptcy court, cutting costs and winning wage concessions from its employees.
The company closed a hub in Dallas-Fort Worth, cut back operations at another in Cincinnati and sold a subsidiary regional carrier, Atlantic Southeast.
But in the end, a major spike in fuel prices ate up much of those savings.
In a statement announcing its bankruptcy filing, Delta said it had been "ahead of schedule" in trying to wring $5 billion in annual costs from its balance sheet by next year, but the effort was "outpaced" by sharply higher fuel costs and price pressure driving down revenues.
"Delta's financial problems are severe, but by no means insurmountable," said Gerald Grinstein, Delta's chief executive officer, in a statement, informs CNN.