The United States did not invade Iraq because it was threatening to switch to Euros. If anything, American banks would have been thrilled at the prospect of new FX revenues.
> Oil bourses trade in dollars
Oil bourses? Oil futures are mostly traded on exchanges, but oil the commodity is mostly traded over the counter. It's privately negotiated. Those private negotiations reference whatever they want to, whether Brent in USD, Brent in EUR, WTI in USD, COM in JPY, et cetera.
These exchanges trade what is referred to as 'light- sweet' crude oil and a single contract, or 'lot', calls for the purchase or sale of 1,000 barrels of oil. Traders can buy and sell oil for delivery several months or years ahead'