When ever I fly UA, which is very often, I am always given an option to buy more miles. I just did it and I can't decide if it was worth it. Also, how do they calculate the number of miles and the price? It's all over the map, it's not always the same example TATL: J class is 9000 additional miles for $300, or 15,000 for F class for $600, J class to deep South America is 12,000 miles for $400...etc. It's different every time so they must factor the fare you paid: eg; the higher the paid fare the more miles you get and for less? A lighter pax load, so drop price and get more rev for that flight, Perhaps status counts? Are the prices lower and miles higher for Global Services?

So, I flew on a RT $7000 (which was a discounted contract fair) EWR/GVA/EWR in BF and I bought an additional 12,000 miles for $350. In hindsight, to get a saver seat in economy to London is 50,000 (I think) ...I would have needed to buy roughly $1400 in bonus miles to get a "free" flight. Seems like I could get a UA ticket from NY to London for less, if I planned ahead?

It is very enticing to hit that button for $12,000 miles! And is DL and AA doing this too? Have their been any consumer reports done on this?