Is there any rhyme or reason to which markets have the Delta Basic Economy fares?

Delta answers that with a resounding “yes!”, but to the average traveler it isn’t as obvious. These fares were first Introduced in 2012 in just a few markets where Delta went head-to-head with Frontier Airlines. Since then, they have expanded to include routes that have competition from Spirit Airlines as well. As these competitive airlines change their route maps, Delta adjusts to keep pace. No published list of markets exists, but we can report a noticeable increase in the number of flights to/from Baltimore specifically offering Basic Economy.