Pan American’s first jet service to South America was by a flight from New York to Caracas, Venezuela; Asuncion, Paraguay; and Buenos Aires, Argentina on July 20, 1959. Pan Am also intended to serve Rio de Janeiro on this route, but the airport runway there was too short for the Boeing 707. 

This cover was carried on the Foreign Air Mail Route 5 flight from the United Nations Post Office in New York to Buenos Aires, Argentina (where it was backstamped) and is listed in the Jet Age Flights section of The American Air Mail Catalogue as J-127u.