In 1920, O’Neill was appointed by the Mexican Government to train and organize a modern Mexican air force. Upon his return to the U.S. in 1925, he conceived the idea of an airline & mail service connecting the east coasts of North & South America utilizing large flying boats. Following a stint in 1927 as the exclusive Latin American agent for both Boeing and Pratt & Whitney, O’Neill founded and headed the New York, Rio & Buenos Aires Line in 1929, piloting much of the maiden flight himself in a Sikorsky S-38. After NYRBA merged with Pan Am in 1930, he formed a gold mining company Bolivia. O’Neill retired to the Bay Area in the late 1960s where he lived until his death in 1980.