Seems the agreement people refer to was made in secret. Hasn't been acknowledged publicly or officially from what I have read. mises.org and other sources have mentioned that the agreement has long been ignored and they linked to this article. One of the few establishment outlets that actually acknowledge its existence.

I would call this petrodollar agreement a conspiracy theory in its purist form. Most likely one that is true based on what we have witnessed since the 70s. I think it is far more likely some under the table agreement was reached than not.