Different airlines charge different taxes/fees
To make things more confusing, different airlines charge different amounts of taxes/fees on award tickets for the identical route and even the identical flights. Several years ago, our family flew to Rome from the east coast on Continental flights connecting in Newark. At that time, Continental was in an alliance with Northwest and Delta. We had our miles spread out over all three airlines and so we obtained our award tickets using miles from each of the three airlines. We were obviously fortunate to get the award tickets, but mysteriously each of the three airlines charged us different amount of taxes/fees for the identical flights on award tickets. The difference was at least $100 I recall and I think the Delta charges were the highest. I could get no reasonable explanation from the airlines for this significant discrepancy.