Delta operated all of its Paris flights (CVG, ATL, JFK) into Orly Airport until
1998, when the routes were transferred to Charles de Gaulle. The transfer
pre-dates Skyteam although Delta and Air France were already in a loose
alliance by the time the airports were switched.
American and Continental were the other two airlines that were operating
to ORY. Continental moved first, followed by American, in October 1999.
American actually resisted the move to CDG because it felt it would not
have adequate facilities to operate effectively there. Paris has been a
hugely profitable destination in Europe for American and the carrier was
probably concerned that it would be competing with United, Continental,
US Air, TWA, and Northwest from the same airport, albeit to different US
Orly Airport was thoroughly inadequate for long haul services. It was old,
cramped, and although close to central Paris, it was not able to offer the
type of connections are rail links available at Charles De Gaulle/Roissy.