Note that you can purchase extra segments in any class at or below the class of your ticket. This is useful when the extra segment doesn't have anything but coach service, for example, or the airline's biz class isn't worth USD300.

Some airlines/agents have allowed this pax to select which segment is "extra" while others have insisted that they be the last in chronological order, an obvious disadvantage when an earlier segment had that low-class service. I don't think there is anything in the rules on this.

Note also that you can have as many open jaws in your OWE itinerary as you want. For example my last ONE included London-Iceland-London. Including both legs in my ONE would have added up to 21 segments; fortunately, I was able to get a GBP39 fare for the outbound leg. That was in coach, but BA biz intra-Europe is nothing to chase after.

I don't know how much the return would have cost, since I didn't have any better plans for the ONE segment. In any case my point is, if you've put together a 20-segment trip and wish for more, or have used the free 4/6 segments in a continent and want more, first check to see which segments can be purchased separately for under USD150 - they abound.