Term which refers to the likeness or least interchangeability of a petroleum product. Material shipped on a pipeline must be fungible, i.e. have a common set of specifications acceptable to various shippers, and the same holds true for futures contracts. The less fungible the product, the less likely it is to succeed in the futures arena and the more problem it is likely to create in the distribution process. Various elements of the Clean Air Act have made several petroleum products less fungible.