Many making the "oil bubble" argument cite the shape of a chart to make their case. For one thing, there’s no shortage of oil; inventories rose a bit this week and remain at just about the middle of the five-year average range for this time of year. Now that the Federal Reserve has signaled it may soon end its yearlong rate-cutting spree, the dollar — whose fall had been a big factor in the run-up of crude prices — is showing signs of strength. And a sluggish U.S. economy and high gasoline prices have begun to make a dent in demand.