I forgot the other big player in the Mideast, Royal Dutch Shell.

Iraq produces about 2 million bbl/day.

A petrodollar is a U.S. dollar earned by a country selling petroleum.
OPEC oil is quoted in dollars, hence a demand for dollars on international exchange markets.

The U. S. dollar is a medium of exchange; Canadian dollar, yen, Euro, whatever have the value assigned by currency traders at the time a transaction takes place.
Canada is the largest oil exporter to use the term "dollar" for its currency, hence these are also termed petrodollars.

Why is the U. S. petrodollar considered important to the American economy? It amounts to a long term no interest loan.

It suits the oil industry to trade in a single currency, thus most oil is bought and sold in dollars.

Iran's market has abandoned the dollar. Others will follow.
The U. S. dollar is still the world's reserve currency, but if the U. S. continues to decrease in world trade, other currencies could take over.

In the Middle East, the backing of the dollar by the Saudis is considered firm, so no change by OPEC is expected.

Russia and China talk about a change, but nothing firm on the horizon at this time.