Every country has its own currency within South America. However, the big exception is in Ecuador, where the U.S. dollar is the official currency. Some souvenir shops and the occasional restaurant, located in heavily touristed areas may accept the dollar.
Your guide will gladly take tips in US$ or Euros as well. However do not give your guide the currency of another South American country. Use only the country’s money, US$ or Euros. In general, credit cards are widely accepted, even for your drink on Copacabana beach! It is always best to use the local currency, which is available from most banks’ ATM’s or paying by credit card.