A commodities exchange is an institution, organization, or association that serves as a market for trading various commodities and derivatives products. Exchanges also serve as a clearing house for the transfer and settlement of the physical commodities underlying most futures contracts. Most commodity exchanges across the world trade in agricultural products and other raw materials such as wheat, barley, sugar, maize (corn), cotton, cocoa, coffee, milk products, pork bellies, oil, metals, etc., as well as in contracts based on them. These contracts can include spot prices, forwards, futures and options on futures. Other sophisticated products may include interest rates, environmental instruments, swaps, or ocean freight contracts.