> because all transactions for oil anywhere in the world are dollar-denominated

This was sort of true in the 1970s only because we ignored the Soviet Union and its allies, which included a lot of petroleum production. It's totally untrue now, in a world where America exports oil. (I traded contracts in Connecticut in the early 2010s. Oil was priced in all sorts of currencies. British and Norwegian oil, for example, is sold for local currency.)