Originally Posted by jbcarioca

The actual FX transaction is usually made (practice varies by issuer,country and acquirer) by the first processor in the issuers currency. In general those rates are near typical interbank exchange rates when the transaction is processed, which also varies. The typical variation MC, V and AE are mostly a result of timing. All three make profit on FX, but generally well within typical corporate rate bands. The historical 1% of MC and V also was an arbitrary charge in increase profits.