CHICAGO — Passengers are more dissatisfied with airlines' customer service than they have been in years, at a time when carriers are charging more and more for tickets and services.

An annual survey being released today by the University of Michigan found customers giving airlines the worst grades since 2001, with the industry's overall scores dropping for the third straight year.

United Airlines and US Airways Group Inc., which are in talks to potentially combine into a single carrier, finished next-to-last and last, respectively, in the university's American Customer Satisfaction Index.

A familiar bright spot in the results was Southwest Airlines Co., which led the industry in passenger satisfaction for the 15th consecutive year.