Makes sense for them:
1. Not much they can spend these dollars on. Trade restrictions and such.
2. Transactions with USD can be more easily monitored by the US government, so definetly a minus for Iran.
3. USD has been sliding for a while now.

I would be interested to see oil price relative to say euro. Has price of oil really went up or is just reflection of weaker dollar (in other word inflation for dollar priced goods)?

Hi: If the US dollar had kept its high value against the Canadian dollar reached in 2002, oil would be $47 right now.