Denver, CO DEN to San Diego, CA SAN flight with United

SkyWest Airlines is a major North American regional airline headquartered in St. George, Utah. It operates flights for larger carriers such as Alaska Airlines (as Alaska SkyWest), American Airlines (as American Eagle), Delta Air Lines (as Delta Connection), and United Airlines (as United Express). SkyWest is the largest regional airline in North America by fleet size, passengers carried, and destinations served. The airline connects passengers to over 250 destinations across the United States, Canada, and Mexico, primarily linking smaller airports to major airline hubs. SkyWest's fleet consists of regional jets, including the Bombardier CRJ series and Embraer 175 aircraft.

Alaska Airlines, headquartered in SeaTac, Washington, is a major U.S. airline and the fifth-largest in North America by scheduled passengers carried as of 2024. Along with its regional partners, Horizon Air and SkyWest Airlines, Alaska Airlines operates a route network primarily connecting cities along the West Coast of the United States, including Alaska and Hawaii, to over 100 destinations in the contiguous U.S., the Bahamas, Belize, Canada, Costa Rica, Guatemala, and Mexico. The airline is a member of the Oneworld alliance, offering passengers access to a broad global network. Alaska Airlines is known for its customer service and loyalty program, Mileage Plan, and offers First Class, Premium Class, and Main Cabin seating options. The airline's primary hub is Seattle-Tacoma International Airport. In 2024, its parent company, Alaska Air Group, acquired Hawaiian Airlines.

Frontier Airlines is a major American ultra-low-cost carrier headquartered in Denver, Colorado, operating flights to over 120 destinations across the United States, Caribbean, Mexico, and Central America. Known for its "Low Fares Done Right" philosophy, Frontier focuses on offering affordable travel by allowing passengers to choose and pay only for the services they need, such as seat selection or baggage. The airline is also recognized for its commitment to fuel efficiency, claiming to be "America's greenest airline" due to its modern, lightweight aircraft and operational practices. A distinctive feature of Frontier is the animal featured on the tail of each aircraft, highlighting North American wildlife.