Southwest Airlines said it plans to sublease all 88 of its Boeing 717s to Delta Air Lines.
The agreement is subject to conditions including ratification of a tentative deal by Delta pilots, and provides that Delta would take three twin-engine 717s a month over three years, starting in the second half of 2013.
Delta said the 100-seater 717 would mainly replace older DC-9 planes and 50-seat regional jets which became less efficient to operate as fuel costs rose.
Atlanta-based Delta also said the tentative agreement its pilots will vote on will enable it to acquire larger two-class, 76-seat regional jets to improve its US fleet as the 717s are delivered. Delta plans to increase the number of those regional jets to 325 from 255, it said.
Southwest added the 717s to its fleet of Boeing 737 narrow-body aircraft when it acquired AirTran last year. The discount carrier had made clear that the 717s did not fit in its longer-term fleet plans.