Round trip vs. one way
 

The only real disadvantage to 2 OW vs RT is that if there's a trip in vain situation, ie you're outbound is canceled or delayed such that there's no point in taking the trip anymore, you'll likely be out the $ on the return ticket.

Nope. I do this almost every single time.

Advantage is that if you have to change it's one change fee vs. two.

Disadvantage is that if the outbound is cancelled or ridiculously delayed you can't cancel/change the return.

If you have to entirely cancel the outbound portion of a round trip, AA (at least for me in the past, you can check on this) will allow you to retain the return, as opposed to the usual rule that if you miss one segment, the entire rest of the trip is cancelled.

I often have situations where I know when I want the outbound but am not yet sure of the return, so I book the outbound.

The change fee issue does not apply because OP is on a BE ticket (I presume that's what he meant by "E-".)

In this limited case, the sole difference is either trip in vain or simply shifting an entire trip by a day, e.g. depart one day later and push the return by a day.

While cancelling the outbound won't affect the return, it's worth remembering that the return is inflexible, so you may simply wind up forfeiting it.

I've been burned once, booking BE tickets for my brother. I booked it as a round trip, he needed to leave one day later due to work commitments. Since I booked the entire ticket as one round trip, I had to forfeit the entire ticket. Couldn't split the ticket after the fact either.

If there is even a remote possibility that you will need to change one or the other, and trip in vain isn't a tremendous concern, then book two one-ways.

On domestic flights, generally yes. On international flights, not necessarily. So it's best to double check on flights with any international component, rather than assuming that this is always the case.

I have been meaning to ask about this.

In general, my experience with domestic flights or international Caribbean fights is about 50% the one way 2X - RT price is the same. The other 50% the RT trip is slightly less. Maybe $75 - $150 (ish) less on a $900-$1300 total. Usually not enough difference to make me give up the flexibility of two one-way tickets.

Recently though looking at different combinations of using miles and / or buying a tickets including international destinations and have come across one way - round trip pricing differences that are extreme. The destination I recall without looking back at my travel notes in Santiago (there were several, but this one I remember as the trip is more likely to happen than the others and I'm actively looking into planning). F to/from SCL to any major US hubs (MIA, LAX, DFW). The one way F tickets are upwards of $6K-$7K. But the RT's in F are $4K-5K. Priced several far out dates and pairs; all showed this characteristic. Anyone know why this is?

LATAM, AA's oneworld partner in South America, does this for all business class fares to/from the US too. The one-way can be more expensive than the whole round trip, which is extremely annoying when you've booked a one-way business award but are having trouble finding a return business award redemption. Your best bet in that case might to get a "business" fare for cheap on a non-AA-partner airline connecting you in northern South America or Central America but with a daytime trip which makes the domestic-style "business" seats perhaps more tolerable than they would be for an overnight trip.

Thanks SDS, that's a thought. Even out right paying for tickets one way back from SCL on AA metal is frustrating and vexing.

For example, October 1. (or basically any date around this time). The OW Ticket Price on AA metal from SCL to DCA in F/J is $6025. That's AA's "flagship" non-stop flight from SCL to MIA, with a tight connection to DCA from MIA. (2.5 hours, probably doable, but tighter than I would like.) Priced each leg individually, the SLC-MIA leg is $3412. The tight connection MIA-DCA flight is $775. Hello. That's $4817. I waste as much $$ for convenience as the next person (or more), but ~ $1200 is not chump change. The next MIA-DCA NS, with a reasonable connection time, is $575. That's A $2000 difference? ($$2000.00!) If I decide to take this flight, absolutely I would book two separate tickets and suck up the annoyance of going back through security. While thinking about what I'm going to do with my $2000 dollars savings.

Is there some logical reason AA is pricing one way flights in this manner on these routes? It seems so absurd I keep thinking I must be screwing up the searches or am missing something.

Long haul flights (Europe, S. America, Asia to a lesser extent) have priced one-ways like this since the beginning of time. Generally speaking it's usually absurdly expensive (compared to the roundtrip) to buy a one-way ticket to/from the US to Europe, S. America, etc. This is nothing new.

The pricing variance you're seeing between SCL-DCA and SCL-MIA is also nothing new or unusual, but a different issue all together. DCA and MIA are different markets, different demand, different competition etc., so airlines will price these differently, even though you may be on the exact same flights for some/all of the trip. If you can save $2k by booking separate tickets then by all means I'd do that. I do that type of thing on 75% of my int'l trips I'd say.

That said, what is the roundtrip price for SCL-DCA? I would just book a roundtrip with the return at a date way off in the future when you may be able to fly it. If you can't fly it, just throw away the return, or hope for a schedule change and ask for a refund, rescheduling, etc. There are lots of options.

It is common among legacy carriers (not just AA) and is a form of fare discrimination based on the fact that these one-way fares are generally purchased by business flyers who may not know when they will return or who can frequently require last minute changes. These business flyers tend to be less price sensitive than leisure flyers who generally plan further ahead and know both outbound and return dates and thus will purchase the cheaper roundtrip fares. This used to also typically be the case on domestic flights before the growth of the LCC's like Southwest. Southwest fares are all priced as one-way's and the legacies have generally matched these on routes where they compete. Although you can still find domestic routes where the legacy carriers have roundtrip fares that are cheaper than two one-way's.

Thanks JJeffrey and Xllioper; much appreciate your detailed replies and background info. I live just outside of DC and used to travel extensively for work, but all domestically. The past few weeks have been my first foray into award flights for "true" international destinations. (Vice Caribbean, Mexico, Canada). All my recent travel outside the US has been Hawaii and Caribbean with not much differential on the one-way versus round trip pricing differential. I do recall the days of one-way tickets being more than RT domestically - showing my age - but did not know the long haul pricing still followed that model. I did suspect the root cause on F/J ticket price and award availability was the DC international business market, but was unprepared for the sticker shock of the differential in U.S. markets pricing the international flights. My perspective on best use of my remaining award miles versus dollars has greatly evolved in the past week for sure.