According to the pilot group, it's FedEx, UPS, Delta, American, and United.

Management will argue that Atlas is no FedEx, but when I am flying FedEx freight in a 747 from a FedEx hub to another FedEx hub using a FedEx call sign, it's pretty hard to say we do something less than what FedEx pilots do. And as the carrier of a significant part of DHL and Amazon freight, I'd say that Atlas pilots are on the leading edge of the primary competition to FedEx and UPS. Of course, not yet mentioned is the array of oddball military, specialized (Dreamlifter), and off the grid flying that we do into places you have to find with Google Earth!

According to Atlas management, it's Southern, Omni, and ATI.