The giant tankers anchored along the Scottish coast in the Firth of Forth weren’t going anywhere. They were just providing floating storage because there was no demand for their cargo, North Sea crude oil. But the flickering computer screens in the world’s trading rooms told a different story. Prices through the month of April were jumping, showing someone was buying, stunning traders and leaving some with heavy losses. That wasn’t the only bizarre gyration last year in the market for Brent, whose price determines the cost of just about every petroleum-based product, from jet fuel to plastic spoons. Such unusual moves damaged confidence so much that some traders retreated from the market. The buyer on virtually all those occasions was Royal Dutch Shell Plc, according to interviews with two dozen industry […]