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What ETF best tracks the price of gasoline, or else crude oil?
There is no ETF that closely tracks oil or gasoline. This is because all existing oil and gasoline ETFs hold futures contracts or other derivatives. Storing the oil and gasoline would be prohibitively costly. Futures contracts are prone to contango and backwardation, sometimes resulting in large deviations from the price of the physical commodity. Contrast oil ETFs with metal ETFs, which track nicely. EDIT: See this article about contango. The UNG chart is particularly ugly.