We’ll admit it: Trying to sort out what drives the price of crude oil up or down can be a head-spinning thing. Sabotage in Nigeria? A nasty Hugo Chavez speech? Hope in the Middle East? Demand in India? U.S. inventories high, or low? Well, at this hour the price of oil is down about four bucks, and that’s thanks to…a Tropical Storm in the Gulf of Mexico. Huh? Here’s an explanation.