Frontier Airlines, Inc. is a low-cost airline headquartered in Denver, Colorado, United States.^[1] The carrier operates flights throughout the United States, Mexico, and Canada.^[2] Frontier is a major low-cost airline with two thirds of its US destinations west of the Mississippi River. The carrier maintains its sole hub at Denver International Airport, and provides regional service to the surrounding Rocky Mountain States through a code-share agreement with Great Lakes Airlines. Frontier is not a member of any of the major air carrier alliances.