Free-market freighters carry a variety of cargoes, between numerous ports. In many instances, the services of these ships are matched with cargoes of brokers who meet on a trading floor in an environment analogous to a stock exchange or a commodities exchange. In times of low freight rates, a broker representing cargo interests may charter a ship for a future date, while having no cargo in prospect but expecting to resell the contract when the rates rise. Most of the world's chartering business is carried out in the Baltic Mercantile and Shipping Exchange, commonly known as the "Baltic Exchange", located in London. Other exchanges, especially for special cargoes, are in operation as well. A large part of the immense world oil transportation business, for example, is chartered by brokers who are based in many different ports.