 However, the actual "cost" of the swap contract would be some small fraction of the minimal $4.5 million in interest payments.The difficulty of determining exactly how much this swap contract is worth, when accounted for on a financial institution's books, is typical of the worries of many experts and regulators over the explosive growth of these types of instruments.Contrary to common belief in the United States, the largest financial center for derivatives (and for foreign exchange) is London.