Using the Citibank debit card in South America is OK if you can find a Citibank ATM. However when I was in Peru, Chile and Argentina this was almost impossible. The gouging banks there charged around A$6 ATM fee per withdrawl and only dispensed a maximum of around A$400 or less per day. As well many merchants in Peru would not accept Mastercard, only Visa. Best to carry USD cash when visiting many parts of South America, A$ notes attract a lousy exchange rate or sometimes were not accepted.