Many carriers when you begin your travel in Europe charges additional Fuel Surcharge on Awards. BA charges fuel surcharge regardless of orgin of transatlantic flights. A DL roundtrip SEA-AMS would be 60000 miles but $47 taxes, whereas DL roundtrip beginning in Europe, AMS-SEA would cost 60000 miles and $330 in taxes. (Note that DL is not a AS partner) An irony is that if you book two one-way SEA-AMS and AMS-SEA, it'll cost you 30,000 miles and $6 tax for the first, 30,000 miles and $180 for the return. Net saving of almost $150 if you had booked a roundtrip originating in Europe. One-way booking, however, might comes with an extra immigration surprise/scruitiny as you might need to provide proof or details of your outbound return flight.

Airport fees are usually highest to London. Pointswithacrew does a good job in identifying airports in Europe with fees.

Jiburi