The waterways surrounding this island nation have become home to one of the world’s biggest oil-storage sites. The problem: It is unclear how much oil is in the tankers anchored there. The historic fall in oil prices has created a pileup of inventories, much of it stashed in tanks in the U.S. and other industrialized countries that are committed to disclosing the latest tally. But millions of barrels are also flowing to locations outside the scope of industry trackers. Some countries, such as Russia and China, choose not to report their oil-storage levels. And traders and oil companies that park supertankers have no obligation to make public their supply. Their decision to keep this information private doesn’t violate any international laws or agreements. But it makes for a more-cryptic and volatile oil market, analysts say. How much crude is in these locations, and how quickly it can be resold […]