Because oil is traded in dollars and is so essential to the global economy, economies have a strong incentive to invest their savings in dollar-denominated assets. Businesses want to save their money in the currency that they need to trade in. Central banks need to build dollar reserves to function as lenders of last resort.Saudi Arabia agreed to sell its oil in dollars and invest its profits in dollar-denominated assets in exchange for American security guarantees. The rest of the Gulf Cooperation Council ...