Some interesting answers in Quora for your questions. We at Future.Travel problematically program our system to search out the cost difference between two 1 way tickets and a round trip ticket for an itnerary. More than a million combinations done in a few seconds. Here is what we found… about 20% of the time it is cheaper to book two ways than it is to book a round trip. This generalisation applies to both Domestic and International ticketing. In the industry this phenomenon is utilised by what is referred to as split ticketing.

Of course timing and routes come into play, with some routes being completely monopolised by 1 or two players. They are focused on profit for themselves and not the buying public.

For Multiple ticketing the same rule applies where you can go from point A to point B, skip over to point C and then return to point A. All on one ticket. You would buy a separate ticket for Point B to Point C. Like this (A-B C-A) as one ticket and (B-C) as a second ticket. Much cheaper in many cases than buying a (A-B-C-A) ticket. In the industry this ticketing is called Open Jaw ticketing and is used by agent to save customers a lot of money. Many OTA’s offer this booking system as an option for the public.