OPEC has priced *all* the oil they sell in US dollars for a while now (since 1972?), and this has helped the US economy, because everybody has to buy US dollars before they buy any oil. And many of the oil exporters have made reciprocal deals with the US to buy our military arms, in a sort of quid pro quo. So, we have been funneling dollars to our military industrial complex; which is not a very productive thing to do.
Interestingly, Iran was the first to sell oil in Euros, and then North Korea started doing all their trade in Euros -- this is probably why they were included in the "Axis of Evil"?