Just about every college kid who’s flown to Europe knows that when they land they’ll be able to get a beer without the fake ID they paid too much to acquire from their neighbor’s creepy older brother. But can those under-21 travelers drink during that flight? Depends on the airline. 

Conde Nast Traveler reports that most airlines set a minimum drinking age that corresponds to the standard booze-purchasing age for their home country — regardless of which direction they are flying.

For instance, American Airlines — which is based in Texas — will only serve alcoholic beverages to customers if they’re 21 years of age or older, even if the plane is over international waters and headed to a country with a more generous minimum age.

Delta, United, Alaska Airlines, Virgin America, Southwest, JetBlue, Spirit, and Allegiant also follow U.S. laws, only serving adult beverages to those 21 and older.

Airlines overseas tend to follow similar rules, CN Traveler reports. For example, Iceland-based WOW Air adheres to the law of its land, serving customers 20 years or older no matter where they’re flying from.

A number of airlines — Mexico’s Interjet, British Airways, Australian carrier Qantas, and Dubai-based Emirates — set the lower minimum age of 18 on their flights.

CN Traveler reports that Air Canada takes a bit of a different approach: While the drinking age is 18, younger passengers on some international flights can partake in a libation if they are given express consent by the guardian or parent accompanying them.

As always, cabin crew on any aircraft have the final authority in determine when anyone of any age has had enough to drink.

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