Portugal is highly accessible for US credit card users, and you will find that Visa and Mastercard are accepted almost everywhere, from high-end hotels in Lisbon to small cafes in the Algarve. However, American Express (Amex) and Discover have much lower acceptance rates and are typically only usable at major international hotel chains or luxury retailers. A critical technical detail to remember in 2026 is that Europe uses the "Chip and PIN" standard, whereas many US cards are "Chip and Signature." While most Portuguese terminals are programmed to recognize US cards and will automatically print a signature slip, you may encounter issues at unattended kiosks, such as those at train stations or gas pumps, which often require a 4-digit PIN. Additionally, always check if your card has No Foreign Transaction Fees to avoid a 3% surcharge on every purchase. If a merchant asks if you want to pay in US Dollars or Euros, always choose Euros (local currency) to avoid "Dynamic Currency Conversion" fees, which provide a significantly worse exchange rate than your bank would.