ATLANTA - Bankruptcy can be a wake-up call for airlines about the need to run their operations more efficiently, but it also can shine a light on a more basic challenge - making customers happy.

UAL Corp.'s United Airlines and Delta Air Lines Inc., both of which restructured under Chapter 11 in recent years, ranked last and next-to-last, respectively, among airlines in terms of customer satisfaction in a survey to be released today by the University of Michigan.

Marks were only slightly better for AMR Corp.'s American Airlines, which teetered on the verge of bankruptcy before winning employee concessions in 2003, and Northwest Airlines Corp., which is currently in bankruptcy.

The airlines said they were working to improve the experience of their customers.

"We know the service is not where it should be as far as baggage delivery," said Betsy Talton, a spokeswoman for Delta, of Atlanta. "We're concentrating on that this year so that we see significant improvements."

Tim Wagner, a spokesman for AMR, of Forth Worth, Texas, said there wasn't much the airlines could do when weather delayed flights.

"The one thing we can do is focus on the things we can control, and that's our face-to-face interaction with customers," Wagner said.

There were some bright spots for a few airlines in the survey. Southwest Airlines Co., of Dallas, ranked first in customer satisfaction. It was one of only two airlines mentioned by name in the survey that improved in terms of customer satisfaction this year compared with last. Continental Airlines Inc., of Houston, was the other.

"We've done as well as we have up to date by making sure our customers have a rich experience, and that's largely due to our people," said Beth Harbin, a spokeswoman for Southwest, which also is one of the few consistently profitable airlines.

The survey, taken in the first quarter of this year, asked 20,000 people to rate their level of satisfaction as customers of companies in a variety of industries, including the airlines.

An American Customer Satisfaction Index, on a scale of 1 to 100, was created based on the responses to questions about overall satisfaction, intention to be a repeat customer and perception of quality, value and expectations.

The index for the airline industry as a whole fell to 63 from 65 last year. US Airways lost ground in satisfaction, falling to an index level of 61 from 62 last year. US Airways is the dominant carrier at Philadelphia International Airport, with about 60 percent of the traffic. Weather problems in February and in March, plus problems with US Airways' reservations and ticketing system in March, caused extensive flight cancellations and delays for the airline. Southwest had the highest index with 76, up from 74 last year. United's was the lowest at 56. Slightly ahead of that were Delta at 59 and American at 60. Northwest, of Eagan, Minn., was only slightly better at 61.

"The same problems that have pulled airline passenger satisfaction down the past few years - disenchanted employees, increasing fuel costs, bankruptcy, and now also record levels of lost, delayed, and damaged luggage - cause it to drop again," the researchers said in their analysis.