[BlowFish]

You buy (or sell) the contract on credit. You provide margin (a deposit) against potential losses. Exchanges have a margin requirement based on volatility and point value of the instrument being traded. The overnight margin is often more than the daytrading margin (more risk). Many brokers do there own risk analysis and allow you to trade with lower margin deposited. Dont be tempted to trade over leveraged just because they allow you to! With futures accounts are usually settled at the end of the day (google settlement) essentially money is transferred from the losers accounts to the winners accounts. This is one of the reason you have brokers as they organise the settlement of customer accounts (though some clear through a third party).