Can I pay in US dollars at the Triple Frontier?

Direct answer: It depends which side of the border you are on. In Paraguay the dollar is the currency the shops actually work in and usually gets the best price. In Argentina it is accepted in part of the tourist trade, but the parallel-rate gap has fallen to 0.3%-1.6% and the advantage is gone. In Brazil shops work in reais and are not obliged to accept dollars.

It looks like one question and it has three answers, one per country. Same trip, same day, and the currency that solves the problem changes every time you cross a bridge.

Paraguay (Ciudad del Este): the dollar wins

Trade in Ciudad del Este is organised in dollars. Electronics, perfume and computing are usually priced in that currency, and paying in dollars avoids two conversions: yours and the shop's. Many stores still add a cash discount.

What to watch in practice:

• Notes must be in good condition. Torn, written-on or heavily worn bills are often refused, and older series sometimes fetch less.
• Change comes back in guaraníes. On odd amounts you will usually get local currency at the shop's own rate. Carrying smaller notes reduces the loss.
• Ask for the final figure before closing. Every shop applies its own conversion rate.

The cheapest order there is usually: dollars in cash, Pix, card, reais in cash. The full comparison is in paying with reais or Pix in Paraguay.

Argentina (Puerto Iguazú): accepted, but no longer clever

Part of the tourist trade in Puerto Iguazú takes dollars, always at the shop's own rate, which varies from door to door. For taxis, buses and small shops, pesos remain more practical.

What changed is bigger than it looks. For years the advice was to carry cash dollars and change them on the parallel market, because the gap to the official rate paid for part of the trip. That gap has all but closed.

We track it daily. In the two weeks to 11 September 2026:

At that spread, carrying cash purely for the parallel market no longer pays: the gain does not cover the risk or the cost of two conversions. The measurement stays live at exchange rates now, because this can change again.

Brazil (Foz do Iguaçu): reais, full stop

Restaurants, hotels, supermarkets and shops in Foz work in reais. No business is required to accept foreign currency, and the few that do apply a rate well below the exchange house next door. If you arrive with dollars, change them before you shop.

On 11 September 2026 the commercial dollar was at R$ 5.11.

How much cash to carry

There is no single number, but there is a rule of thumb: cash for Paraguay, card or Pix for everything else. The big purchase in Ciudad del Este is where cash earns its keep. In Foz and Puerto Iguazú a card covers almost everything without making you carry a large sum.

Where to change money, with the spread explained note by note, is in where to exchange money at the border.

Summary by country

Source: our own exchange-rate measurement (Marco Três daily series of official and parallel dollar, plus counter readings in Ciudad del Este) and the commercial rate of 11/09/2026.