Here are the results of a small experiment I made with foreign exchange on credit cards. On 12/27 I made identical charges in the amount of R$12.27, in the currency of Brazil (the ‘real’), to my MBNA American Express card, my MBNA Fidelity MasterCard, and my CapitalOne VISA. Both MBNA American Express and CapitalOne VISA claim to charge only a 1% exchange fee. In the case of MBNA Fidelity MasterCard, telephone representatives usually say the fee is 3%, but sometimes they say 1%. All of these cards offer cash rebates: CapitalOne is 1%, MBNA Fidelity is 1.5%. MBNA AMEX varies from 1% to 1.5% depending on its color and in some cases offers double rebates for travel and entertainment expenses. Here are the results:

MBNA AMEX: $5.29, posted on 12/29
MBNA Fidelity MC: $5.22, posted on 12/28
CapitalOne VISA: $5.22, posted on 12/28

The exchange site oanda.com gave the conversion as $5.24471 using the interbank rate for 12/27, $5.24583 for 12/28, and $5.24352 for 12/29. On the basis of these rates, the difference in posting date for AMEX should have resulted in a slightly lower dollar amount, not a higher one. It remains to be seen, of course, if any of the cards will charge a separate ‘finance’ fee when the monthly statements are printed, but phone representatives I spoke to claim there will be none. For now, AMEX is the big loser, with a 1.34% difference with respect to the other two. MBNA Fidelity would seem to be the winner, since it offers a higher rebate. Nonetheless, the picture would be reversed if MBNA later throws in a 3% fee. And taking rebates into account, AMEX would come out ahead in the case of a travel and entertainment expense.