I've seen the same thing for Chicago to Seattle. And the one time I needed a one-way ticket, I bought the cheaper round trip ticket.

I seem to recall having heard that that can bring you to the attention of Homeland Security. This may not be true, of course. But I have heard that.

I don't know the full story, but I've heard a partial explanation: supposedly airlines want you to buy a round-trip ticket so they can be sure that return flights are, overall, as full as outward bound flights; it makes their planning easier. One-way tickets supposedly increase the chances of some flights having empty seats, and they're trying to discourage that.

Whether this was ever mathematically demonstrated to be efffective, I have no idea. Even if it was at one point, it may not be true any more, given that some domestic discount airlines now offer one-way tickets for half the price of round-trips.

Jon wrote:

"I seem to recall having heard that that can bring you to the attention of Homeland Security. This may not be true, of course. But I have heard that."

It probably would, but the policy of charging more for the one-way ticket was in place long before 9/11. I was researching a one-way flight when I was in college and I ended up buying the roundtrip ticket.

My (incomplete) understanding is that if an airline finds out that you're intending to not use part of a ticket, they get very unhappy, and may even refuse to let you travel with them.

Some friends of mine once tried to travel in such a way that they would end up not using the final leg of their (multi-leg) ticket. IIrc, the airline told them that their luggage would have to be checked through all the way to the final ticket destination, and that it was against the rules for the passengers to intentionally not fly that final leg.

Did you check the fare rules? When the difference is that extreme, it's often because the one-way fare is refundable or otherwise less restricted than the round-trip you're comparing to.

Though sometimes the one-way with comparable rules really does just cost more and the airline is expecting customers to voluntarily follow the rules that say you won't purchase a round-trip intending to use only one leg. They used to expect travel agents to enforce those rules (and would withdraw booking priveleges from agents whose customers routinely violated the rules), but in this age of self-service online ticket purchases, that doesn't work so well.