Originally Posted by
SparseFlyer
So, a potential reason for this is that when you buy SFOYYZ R/T, you book it using fares sold in SFO (even for the return portion). So there might be a discounted fare published for SFOYYZ but not YYZSFO. Booking two one ways means you miss out on the discount for the return.
This is the most likely reason if there's no PROS availability shenanigans, and difference is higher than taxes.
I think the Eastern Canada to FL fares can have this quite often. Many times with the lower fares ex FL.
You're correct. The SFO-YYZ ow fare is $638, whereas YYZ-SFO is $488 (both USD).
But again, the point is to check. If you're departing YYZ, it's easy. If you're departing SFO, two one-ways is cheaper than a round-trip. If you can plan multiple trips together, booking two one-ways and some reverse round-trips between them is much cheaper.
And I'm pretty sure this isn't the nefarious nested/back-to-back ticketing the airlines don't like, since no fare rules are being circumvented.