The United States Post Office Department formally established domestic air mail service on May 15, 1918.   For the next eight years, all air mail was flown on government owned and operated airplanes.  On February 2, 1925, Congress passed the “Kelly Act” which resulted in the conversion of airmail from a government service to a commercial service, known as CAMs (Contract Air Mail).  The first two CAM routes, CAM-6 and CAM-7, started operations on February 15, 1926.   Many CAM routes were established and the contracts for the routes were awarded to many private air service companies.  After May, 1934, the routes became known simply as “air mail routes,” or AM’s (http://www.aerodacious.com/CAM.HTM).

The inauguration of a new air mail route often included ceremonies and souvenirs.  These included first flight covers (FFCs); a cancelled (postmarked) at the point of origin envelope with a special cachet describing the event.  The covers were occasionally signed by the pilot or the local postmaster.  Ideally, the cover should be back-stamped (on the reverse) at the place of arrival, proving that the covers were actually on the flight.  Associated with first flight events were airport dedications.  Envelopes with airport dedication cachet covers were also popular souvenirs.  

These three Louisiana petroleum-related examples are for the Monroe Gas Field (front and back; discovered in 1916), Jennings Oil Field (discovered 1901), and Shreveport (Caddo-Pine Island Field, 23 miles northwest, discovered in 1905.

SPENCER, Jeff and MILLER, Byron, 2001, 100 years of exploration and production at Jennings Field, Gulf Coast Association of Geological Societies Transactions, v. 51, p. 305-312.

SPENCER, Jeff A., and MILLER, Byron, 2003, Jennings Oil Field:  the start of Louisiana’s oil industry:  Oil Industry History, v. 4, p. 13-19.

SPENCER, Jeff A., 2013, Pennsylvania petroleum philatelic event covers, Oil-Industry History, v. 14, p. 43-48.

SPENCER, Jeff A., 2015, Oklahoma petroleum philatelic event covers, Oil-Industry History, v. 16, p. 123-128.