Originally Posted by
NYC Flyer
Basic fares cannot be combined with main cabin/premium/business fare types. You'll have to call DL or a travel agent.
Use of one-way fares in this scenario is likely to significantly exceed the upcharge to main cabin on a roundtrip ticket that combines two fare types.
An agent wouldn't likely be able to override the combinability restrictions on BE fares. It's not just a website issue. The difference between roundtrip and one-way BE fares can be fairly minimal. In the above case, one-way BE fares are only $15.50 more than roundtrip BE fares ($16.00 vs. $0.50). Although on JFK-LHR, the difference looks be over $100 which is more than the difference between main cabin and BE. I'd suspect one-way PE fares will likely be significantly more than roundtrip PE fares. Ultimately, there's probably few to no cases of PE and BE one-way's being cheaper than PE and main cabin fares booked on a roundtrip basis to get roundtrip fares (assuming you meet the advance purchase and min stay requirements of the roundtrip fares).