Fiat currncy is backed by both gold and oil deposits, so it is not impossible that petrodollar exists. This is what I think about why USA has attacked Osama Binladin because he doesn't want to share their oil deposits to them. And because of that he has faulted by US government about terrorism.
Fiat is not backed by oil or gold, it backed up by bonds, another form of paper. Don`t live in illusions, educate yourself. US gold standard ended in 1971. Oil is priced in dollars, its like that cause several big oil producers have currencies pegged to US dollars. You can read more about it on internet, you have many public informations about that, so educate yourself.
In near future we will see some changes on that field, as I`m reading China and Russia along with some other countries are working to break that down, we will see what will happen, it`s to early to say anything about what will happen on global stage.