Delta Airlines
Fare	Domestic	Internation	Description
A	First Class	NA	Discounted Domestic First class. Make sure to assign yourself a seat if booked in this class.
B	Yes	Yes	Coach, Upgradeable transoceanic & domestic (also eligible for D511 mileage award domestic upgrade)
C	NA	Biz Elite Fare	Business Elite Latin America (domestic first class seat, Business Elite service)
D	Biz Elite Fare	Biz Elite Fare	Discounted Business Elite transoceanic and domestic (limited markets)
E	No	No	Coach travel, promotional / contest awards no mileage accrual, no upgrades
F	First Class	NA	First Class Full fare - also used when involuntary rerouting any fare class passenger in First due to bumps, irregular ops, etc.
G	via PMU	NA	First Class, Domestic upgraded via Platinum Medallion Upgrade, North American Upgrade or Upgrade Points award
H	Yes	No	Non-upgradeable transoceanic, UPGRADEABLE domestic (no mileage award upgrades)
I	Biz Elite Fare	Biz Elite Fare	Published deeply discounted promotional business class fare, also non published promotional or convention fare in business class
J	NA	Biz Elite Fare	Business Elite transoceanic full fare - also used when rerouting any fare class passenger in BE due to bumps, irregular ops, etc.
K	Yes	No	Non-upgradeable transoceanic, UPGRADEABLE domestic (no mileage award upgrades)
L	Yes	No	Transoceanic or domestic (deep discounted fare)
M	Yes	Yes	Upgradeable, transoceanic & domestic (also eligible for D511 mileage award domestic upgrade)
N	No	No	Coach Points Award - non-upgradeable - no mileage accrual on award tickets
O	NA	Biz Award	Business Elite Points Award - no mileage accrual on award tickets
Q	Yes	No	Non-upgradeable transoceanic, UPGRADEABLE domestic (no mileage award upgrades)
R	First Award	NA	First Class, Domestic Award - - no mileage accrual on award tickets
S	No	No	Non-upgradeable, transoceanic or domestic - consolidator fares. Generally changeable without fee through your booking agent (e.g. tour group). These are NOT priceline fares ... they are fares purchased by a consolidator valid on any number of flights, generally international, for coach travel.
T	Yes	No	Transoceanic or domestic New lowest fare typically for fare matching competitors. Senior Select program fare, used for several promos (i.e. "DL loves NYC" ).
U	Yes	No	Coach (discount web fare. domestic and appears to be international too.
V	upgrade	NA	First Class, Domestic upgraded via Segment upgrade
X	upgrade	NA	Business Elite Domestic & Business Mexico upgraded via Segment upgrade (the Mexico flights are domestic First Class cabins coded as "Business")
Y	Yes	Yes	Full Fare coach, Upgradeable transoceanic & domestic (eligible for D411 mileage award domestic upgrade) - also used when involuntary rerouting any fare class passenger due to bumps, irregular ops, etc. which could allow an originally non-upgradeable domestic fare to be upgraded after the reclassification (if you are lucky enough to find available inventory under these conditions)
Z	NA	PMU or miles	Business Elite, transoceanic and domestic when upgraded via Platinum Medallion Upgrade or Points award

Code	Description
X	Coach
X	First / Business Elite
Yes	Fare is Upgradeable
No	Fare is NOT Upgradeable
NA	Not Applicable
?	Unknown - To be determined