I just called Citibank Diners Club 1-800-2-DINERS, Citibank Hilton HHonors 1-866-517-7795, and Citibank AAdvantage World MaterCard 1-888-766-2484. The first two (Diners and Hilton) said there definitely would be a 3% charge for a US dollar charge outside of the States; the last (AAdvantage) said that there would be no charge. If anybody has the time, give it a try and see what answers you get.