Delta Air Lines has been selling "basic economy" fares" on many of its flights for several years, and is adding the bare bones fares to more of its Mexico routes.

Atlanta-based Delta said it now sells the basic economy fares on more than half of its flights between the United States and Mexico — including to Cancun, Puerto Vallarta, Cozumel and Mexico City — and its partner Aeromexico is also introducing a “Basic” fare.

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These Fortune 500 companies are headquartered in Atlanta 23. Home Depot -- $94.6 million (2017 revenues) 46. UPS -- $60.9 million 64. Coca-Cola -- $41.9 million 71. Delta Air Lines -- $39.6 million 126. Aflac -- $22.6 million 145. Southern Company -- $19.9 million 180. Genuine Parts Company -- $15.3 million 242. First Data -- $11.6 million 303. SunTrust -- $9.2 million 331. Veritiv -- $8.3 million 353. PulteGroup -- $7.7 million 364. HD Supply Holdings -- $7.5 million 370. AGCO -- $7.4 million 409. NCR Co

Basic economy fares, launched by Delta in 2012, do not allow advance seat assignments, do not allow any changes or upgrades — even for a fee, and put passengers in the last boarding zone.

Delta has gradually expanded basic economy fares on domestic flights, and last year announced it expanded it to more than half of its trans-Atlantic flights and added a first checked bag fee on its basic economy fares to Europe and North Africa.