> 10% over the exchange rate between Pentali Marcograms and US dollars. You know oil producers trade in dollars, right?"
You are off by three orders of magnitude, which is pretty amazing.
Forex markets have incredibly tight spreads measured in pips, say 1-4 pips, where 1 pip = 0.0001.
The reason why dollars are important is that people store the results of their oil sales in USD assets. What a good is purchased with means nothing. Where you store the proceeds of the sale is what counts.
This goes to that oh-so-tired phrase 'petrodollar', which many autodidacts misuse to signal a lack of understanding of both forex markets and oil economics. What "petrodollars" means is the dollar holdings that oil exporting states maintain. It does not refer to the currency oil is purchased in. It comes from eurodollar, which signifies dollar holdings in Europe, and not the purchasing of European goods with dollars.
Once we get that definition right, we understand it as a synecdoche for US hegemony in reserve currencies -- e.g. where foreign central banks store their wealth. The actual currency oil is priced in - or anything is priced in - means nothing. What is the point of saving a pip in the forex markets if you are going to be losing .1% in bid/ask spreads when you try to store your wealth in an illiquid bond market? No one -- absolutely no one - optimizes for reducing forex costs when deciding in which nation to park their wealth. They are much more concerned with questions like "Is it legal for me to purchase these bonds? will my wealth be confiscated in the future? What kind of fees do I pay when I buy these bonds?"
The reason the world wants to store their wealth as dollar assets is because the US has a reputation for openness to foreign investment, rule of law, political stability, upholding foreign investor rights, and amazingly deep capital markets that can absorb large foreign inflows with very low spreads. So the bid/ask spread when trying purchase a few billion worth of U.S. bonds is much more important to explaining US financial hegemony than what some random country demands as payment.
I think the no. 1 reason why people get this all wrong is they still want to think we live in a world of specie flows. But there are no bearer assets in international trade - you can't take it with you back home. Your foreign trade profits are going to be stored in some custodial account in some other country. So trusting that country is a big deal. People who think trade is conducted with gold nuggets don't see this custodial account problem, and that's why they don't understand why the U.S. is a global reserve currency. That's when all sorts of conspiracy theories about oil sales, or aircraft carriers, come into play as they try to understand the U.S. role using the ideas they are comfortable with.