In the early 1950s, Continental began several interchange routes with American, Braniff, and United Airlines. Routes were operated on American from Los Angeles and San Francisco to El Paso continuing onto Continental's route to San Antonio and Houston. Continental's Denver to Kansas City route would interchange onto St. Louis with Braniff Airways and United's routes from Seattle and Portland to Denver would interchange with Continental's routes onto Wichita and Tulsa. These interchange routes continued for many years until Continental was able to secure routes of its own between each city.