Delta has ordered 30 additional narrowbody aircraft to support growth plans for its domestic network.
The new Airbus A321neo order will augment the 125 A321neos that Delta already had on order.
The first of the combined 155 planes is slated for delivery early next year.
Delta will configure the aircraft with 20 first class seats, 42 Comfort Plus seats and 132 economy seats.
Competitor United earlier this summer also announced an expansion of its fleet that includes 70 A321neos.