Dount there is much disagreement on Iran being 4th Coatsy - despite minor ripples in the supply chain..
http://www.eia.doe.gov/emeu/cabs/topworldtables1_2.html
There have been verbals over OPEC valuing oil in currencies other than the US$ - for obvious reasons. Last I looked Iran was still a member of OPEC.
The projected effects of OPEC changing currencies is kinda severe for certain nations and would cause considerable economic upheaval and prob a decision not to be taken lightly. The effect on places like the US would be catastrophic.