In the forwards market, contracts are purchased and offered OTC between two parties, who decide the terms of the agreement between themselves. In the futures market, futures contracts are bought and sold based upon a regular size and settlement date on public commodities markets, such as the Chicago Mercantile Exchange . Forex markets exist as spot markets as well as derivatives markets, offering forwards, futures, choices, and forex swaps. An E-mini S&P 500 is an electronically traded futures contract that may be a fraction of the worth of a standard futures contract. Generally speaking, premarket trading operates underneath different rules than regular buying and selling.