Originally Posted by acf573
No magic here. First, as you note later, MC and Visa do have different exchange rates. The currency market isn't really like the stock market where everyone sort of agrees what the current price is. The currency market is a lot more dispersed, and depending on who you ask, you may get a different price. IME they're usually pretty similar, but a small fluctation is certainly not uncommon.
Second, I would guess that your Citi debit and BofI debit transactions posted on different days. 5/22 rate was 2.20, 5/23 rate was 2.26. Why does one post a day later even though it's an internal ATM? Who knows. It just happens that way.
RE: Citi, the exchange rate number they quote you should be with 0% commission. Then they tack on the 1% that you saw. This is if you use a Citi ATM. If you use a non-Citi ATM, they'll tack on 2%.
Actually it is like the stock market, in that if there is any difference in the rate that 2 currency dealers are willing to offer a currency then there is an arbitrage opportunity for risk free profits which would be substantial since currency trades can be leveraged up to 200:1 in some cases. If you can buy a U.S. dollar for .79 euros from dealer A and sell it for .80 euros to dealer B, you just made an instant profit. Any difference in currency rates between dealers, even to the .0001 of a cent are quickly (microseconds) rectified. There would certainly never be a difference as large as a percent between dealers. The difference could be between the realtime quote at 1022 GMT when you made the transaction and the end of the day snapshot that Oanda quotes.