system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why most of round trip tickets are cheaper than one way?
gpt
Domestically they're not.  One way is usually a bit over half as much as a round trip flight.

International is a different story.  If an airline flies you into a country and then that country refuses to allow you to enter, then *regardless of why you were refused entry* the airline needs to pay to fly you back.

There are also very, very few people who fly international one way, so airlines are extremely suspicious about anyone who does.

Because of the risk that international one way passengers pose to airlines, as well as their rarity, airlines just assume that a high percentage of such passengers will be rejected by the destination country and bake the weighted average cost of a return ticket into the one way ticket price.