OPEC sells oil in dollars. It creates a lot of demand for the US dollar. The minute OPEC decides to abandon the dollar for some other currency or basket of currencies the dollar will be hit hard and most likely start to freefall. Most people don't realize how important the sale of oil in US dollars is to the US. GW Bush wanted to go into Iraq not because of WMDs, but because SH started selling oil in Euros. The first thing Bush did was change that back to dollars.