Representatives for the nation's third-largest airline and its pilots union said the two sides continue to negotiate, although they would not say if a deal is possible soon. Meanwhile, 99 Delta pilots retired in September, effective Oct. 1, the union said Monday.

In a research note published Monday, Morgan Stanley airline analyst William Greene advised clients to avoid Delta's shares. The firm estimated Delta will lose $14 a share this year, $3.90 a share in the third quarter alone. Delta reports its third-quarter earnings Oct. 20.

"We continue to believe that absent a pilot deal this month, Delta's liquidity is too low to avoid a Chapter 11 filing," Greene wrote.

He said he thought that that view "is also consistent with management's public statements." Last month, chief executive Gerald Grinstein said that if all the elements of Delta's cost-reduction program are not in place in the "near term," the airline would be forced to restructure through the courts.

Atlanta-based Delta has refused to be more specific on what it means by "near term." Company spokeswoman Benet Wilson declined to comment Monday on the timing of a possible bankruptcy filing. Delta has asked for $1 billion in concessions from its pilots, who have offered up to $705 million.

On the New York Stock Exchange, shares of Delta fell 18 cents, or 5.5 percent, to close Monday at $3.08. The stock has fallen more than 90 percent since the Sept. 11, 2001, terrorist attacks. The day before the attacks, the stock closed at $37.25. The stock is still above its 52-week low of $2.94 posted Sept. 27.

Delta has lost more than $5 billion and cut its work force by 16,000 jobs in the last three years. It said last month that it would cut up to another 7,000 jobs in the next year and a half.

The company staved off a bankruptcy filing at the end of September when it reached a deal with its pilots to allow the company to recall early retired pilots on a limited basis to help ease staffing shortages.

Since Jan. 1, 625 pilots have retired, 505 of them before the normal retirement age of 60, according to the union. Seventy-one of the 99 pilots who retired in September were early retirements, union spokeswoman Karen Miller said.

As of Monday, Delta had roughly 7,100 active pilots and 809 more on furlough, Miller said. The total is down significantly from the roughly 10,000 pilots Delta had at the time of the terrorist attacks.

Thursday, the union said in a memo to pilots that progress has been made on negotiations on changes to work rules and that comprehensive negotiations were expected to resume as early as the next day. The union had no further update Monday. Its board of directors is set to hold its biennial meeting next Monday in Fort Lauderdale, Fla. The union said its negotiating committee will be in Fort Lauderdale as well and will be available to continue to negotiate with management.