Frontier Airlines (F9) is a Denver-based low-cost carrier. The carrier flies to about 65 destinations in the United States, Costa Rica, the Dominican Republic, Jamaica and Mexico. Its fleet of planes each feature a single Economy Class cabin. However, passengers can upgrade to Select Seating, which is located toward the front of the plane, or Stretch Seating, which features more legroom. Frontier's hub is based at Denver International Airport (DEN). An additional eight airports have been designated as focus cities. The airline has a codeshare agreement with Great Lakes Airlines.
After making a codeshare agreement with Lufthansa that went into effect in 2010, jetBlue transitioned to the Sabre reservation system used by Lufthansa, enabling the airlines to sell tickets on each other's flights, transfer luggage and passengers between the two carriers, and combine frequent flyer programs,. By making use of JetBlue's North America routes as a feeder network, the agreement put Lufthansa in a position to operate quasi-hubs in New York–JFK and Boston Logan.