Round-Trip vs. One-Way

• Airline companies use discounted round-trip pricing to discourage travelers from fare shopping and to protect revenue. If one-way tickets were cheaper than round-trip tickets, you would have the option to buy two one-way tickets to and from your destination from the airline offering the cheapest fare. Providing a discount for round-trip travel ensures that one airline company gets both your outgoing and return business.
  
  

Outgoing Leg

• If a passenger uses the outgoing leg of a ticket and does not check-in for the return leg, the airline will simply cancel the remainder of a ticket on the day of the no-show. If an airline company realizes and can prove that you have purposely used a round-trip fare for a one-way ticket, it could flag your frequent flyer account since the practice is considered a breach of its contract of carriage. This could result in the confiscation of frequent flyer miles or penalties. The company could also charge the travel agent that booked your ticket a debit memo, requiring the travel agency to pay the difference of the one-way ticket fare.
  
  To be absolutely sure that the airline company doesn't discover your original intent to use only the one-way fare, you can call and say that you have a family or medical emergency and will not use the return ticket. For good measure, you can even ask for a partial refund, even though the company is unlikely to oblige.
  
  

Return Ticket

• An airline company cannot anticipate whether you will use the return portion of a ticket, which makes it easy to use the outgoing leg of a round-trip ticket. If you do not use the outgoing leg of a round-trip ticket, it makes using only the return leg almost impossible. Most airline companies will automatically cancel a ticket if a portion of the ticket is not used. The airline company will almost always require you to pay the difference and ticket change fee to be able to use only a return flight.
  
  

Airline Ticketing Rules

• Most airline ticketing rules include a section about booking round-trip tickets for one-way travel. The airlines call it throw-away ticketing. Delta airlines ticket rules list the "use of discounted round-trip excursion fares for one-way travel" as a prohibited ticketing practice, while US Airways calls throw-away ticketing an inappropriate booking practice. While the practice is against the rules, it is a rule that is hard to and rarely enforced.