In the mid 1920s, Contract Air Mail (CAM) routes were assigned by the U.S. Postal Service to U.S. airlines to carry mail between U.S. cities. The initial CAM carriers would in time and through mergers and acquisitions go on to establish the foundation of the U.S. airline industry through the creation of key players such as American Airlines, United Airlines, Western Airlines (which would eventually be acquired by Delta Airlines, who was also a CAM carrier beginning in 1934), Boeing, Pan Am, Trans World Airlines (TWA), Northwest Airlines, Braniff, Continental, and Eastern Airlines.
Starting with an initial group of five, a total of 34 CAM routes would eventually be established between February 15, 1926, and October 25, 1930. These are listed below.
| CAM # | Operating Carrier | Route | Inaugurated |
| 1 | Colonial Air Transport | New York NY – Boston MA | July 1, 1926 |
| 2 | Robertson Aircraft Corp | Chicago IL – St Louis MO | April 15, 1926 |
| 3 | National Air Transport | Chicago IL – Dallas TX | May 12, 1926 |
| 4 | Western Air Express | Salt Lake City UT – Los Angeles CA | April 17, 1926 |
| 5 | Walter T Varney | Elko NV – Pasco WA | April 6, 1926 |
| 6 | Ford Motor Company | Detroit MI – Cleveland OH | February 15, 1926 |
| 7 | Ford Motor Company | Detroit MI – Chicago IL | February 15, 1926 |
| 8 | Pacific Air Transport | Seattle WA – Los Angeles CA | September 15, 1926 |
| 9 | Charles Dickinson | Chicago IL – Minneapolis MN | June 7, 1926 |
| 10 | Florida Airways | Jacksonville FL – Miami FL | April 1, 1929 |
| 11 | Clifford Ball | Cleveland OH – Pittsburgh PA | April 21, 1927 |
| 12 | Colorado Airways | Cheyenne WY – Pueblo CO | May 31, 1926 |
| 13 | Philadelphia Rapid Transit | Philadelphia PA – Washington DC | June 6, 1926 |
| 15 | Philadelphia Rapid Transport | Philadelphia PA – Norfolk VA | October 10, 1926 |
| 16 | Continental Air Lines | Cleveland OH – Louisville KY | August 1, 1928 |
| 17 | National Air Transport | New York NY – Chicago IL | September 1, 1927 |
| 18 | Boeing Air Transport | Chicago IL – San Francisco CA | July 1, 1927 |
| 19 | Pitcairn Aviation | New York NY – Atlanta GA | May 1, 1928 |
| 20 | Colonial Western Airways | Albany NY – Cleveland OH | December 17, 1927 |
| 21 | Texas Air Transport | Dallas TX – Galveston TX | February 6, 1928 |
| 22 | Texas Air Transport | Dallas TX – San Antonio TX | February 6, 1928 |
| 23 | St Tammany & Gulf Coast Airways | Atlanta GA – New Orleans LA | May 1, 1928 |
| 24 | Embry-Riddle Company | Chicago IL – Cincinnati OH | December 17, 1927 |
| 25 | Pitcairn Aviation | Atlanta GA – Miami FL | December 1, 1928 |
| 26 | National Parks Airways | Great Falls MT – Salt Lake City UT | August 1, 1928 |
| 27 | Thompson Aeronautical Corp | Chicago IL – Bay City MI | July 17, 1928 |
| 28 | Robertson Aircraft Corp | St Louis MO – Omaha NE | May 1, 1929 |
| 29 | Southern Air Transport | New Orleans LA – Houston TX | January 23, 1929 |
| 30 | Interstate Airlines | Chicago IL – Atlanta GA | November 19, 1928 |
| 31 | Curtiss Flying Service | Chicago IL (Cicero – Grant Park) | June 15, 1929 |
| 32 | Varney Air Lines | Pasco WA – Spokane/Seattle WA | September 15, 1929 |
| 33 | Southern Air Fast Express | Atlanta GA – Los Angeles CA | October 15, 1930 |
| 34 | Transcontinental & Western Air | New York NY – Los Angeles CA | October 25, 1930 |