Interesting thread at http://www.travelingbetter.com/forum...ad.php?p=37109 about the implication of one-way fares when changing the return [ignore the whole thing in the thread about the fare classes being different: it's complete misinformation].

In summary, in markets where fares are filed as one way, in a roundtrip scenario each flight gets priced as a separate pricing unit (in that thread's example SFO-ORD is pricing unit 1, ORD-SFO is pricing unit 2).

The implications is that a change to the return segment is a change of the first flight of the second pricing unit, as opposed as a change of the return flight of the first pricing unit. This leads to generally having to pay the difference between the value of the pricing unit and the current fare as if you just bought it, plus the change fee (currently $150). This compares to the generally more flexible rule that applies to changing a return flight of a roundtrip fare, i.e., as long as availability is present in the same fare bucket, you just pay the change fee (currently $150).

On this market AA files one-way fares to match VX, which also has the policy that any changes requires purchasing a new ticket, but has a change fee that is half of AA's (currently $75) when the change is done online, or $100 otherwise.