E-Fares?
 

Are efares upgradable?

Domestically, yes. No bonus booking miles though.

domestic e-fares are. International are usually not upgradeable as they usually book in K or L.

Any published domestic fares are upgradeable. International e-fares are usually not, since many/most of them appears to be in S/K/T/L, which is not SWU upgradeable. You probably should check the fare class to confirm.

At the fare quote screen near the final dollar amount, you should see some wording such as "NO SWU UG" if the international itinerary is not upgradeable. As mentioned above, domestic E-Fares are upgradeable with any upgrade instrument.