(CNN) Passenger satisfaction with airlines has improved for the second year in a row, according to the J.D. Power and Associates 2011 North America Airline Satisfaction Study released Wednesday.

The study was based on responses from more than 13,500 passengers who flew on a major North American airline between July 2010 and April 2011.

They were asked to grade carriers in seven categories: cost and fees, in-flight services, flight crew, aircraft, boarding/deplaning/baggage, check-in and reservation.

Alaska Airlines ranked highest in overall satisfaction among traditional carriers for the fourth year in a row, followed by Continental and American. US Airways was at the bottom of the list.

Among low-cost carriers, JetBlue Airways received the highest overall satisfaction scores for the sixth year in a row, followed by Southwest and AirTran.

Traditional Carriers
1. Alaska Airlines
2. Continental Airlines
3. American Airlines
4. Delta Air Lines
5. United Airlines
6. US Airways

Low-Cost Carriers
1. JetBlue Airways
2. Southwest Airlines
3. AirTran Airways
4. Frontier Airlines

Full story is available at CNN Travel.