system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why it matters in which currency crude oil is traded.

I mean, we give oil a certain value that can be easily expressed in each local currency. So why should it matter if we trade it in, say South Korean Won?
gpt
When you sell a product internationally, you want to use a currency that is easy to exchange, and that will hold its value well.  That means dollars, euros, yen, pounds, and maybe Swiss francs.

If you are Venezuela and just sold a billion dollars with of oil and took won for it, you are going to have a problem.  No one in Venezuela wants won, and even if you showed up in Seoul money in hand, exchanging that much won at once is going to shift the market and give you a bad rate.

With the other currencies, there are plenty of people locally who want them, and the economies are large enough to absorb as much as you want to exchange.  And since they are so widely accepted, you may not have to exchange them at all, and just use them to buy something else.