system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some countries outside of the US use the US Dollar?

Some countries have replaced their official currency with the US dollar. What's even more confusing, though, is the countries that have their own currency,  but still use US dollars frequently. Costa Rica, for example, has their own currency, but they often use USD to pay for things. It's not even limited to the tourist attractions. What's the point of using a foreign currency when you have your own? Is 1 US Dollar really that much better than 550 Costa Rican Colones?
gpt
There are two specific reasons:  

First - oil is bought and sold on the open market in US dollars.  So when Saudi Arabia sells oil to France - France has to use US Dollars to buy the oil from Saudi Arabia.  

Russia, Iran, and China are trying to move away from the petro-dollar for this reason - so they don't have to have US dollars on hand.


Second - certain countries experience hyper-inflation - to the point that Zimbabwe issued 100 trillion zimbabwe dollar notes.  Because of this - the people would lose faith that they would not be able to purchase goods in the international market with their domestic currencies.  So if a baker wanted to import wheat from Egypt - the Egyptian merchant might say, "I won't take Zimbabwe money - I'll sell it to you in dollars."