Chapter 29: Introduction to Index Option Products and Futures 509 
one is bidding for futures at a price of 1401.50 and a trade is printed at 1401.40, then 
he can be certain that he has bought his contracts. 
Futures exchange members who trade mainly for their own account from the 
ring or pit are known as locals." They are somewhat akin to the stock option market­
maker in that they may take the other side of public orders. Note, however, that they 
do not have to make a public market as market-makers do. 
MARGIN, LIMITS, AND QUOTES 
Futures contracts are traded on margin and are marked to market every day. 
Generally, the amount of margin required is small in comparison to the total size of 
the contract, so that there is tremendous leverage in trading futures. Anyone trading 
the futures must deposit the initial margin amount in his account on the day he ini­
tiates the trade. Then at the end of each day, the amount of gain or loss on the con­
tract is computed, and the account is credited if there is a gain or debited if there is 
a loss. In case of a loss, the trader must add more cash to his account to cover the 
loss. This daily margin computation is known as maintenance margin. Treasury bills 
or other securities are good collateral for the initial margin, but the daily variation 
margin is required in cash. 
Example: The S&P 500 futures contract is a cash-based futures contract that trades 
on the Chicago Mercantile Exchange. Since the contract is settled in cash, there is 
no actual physical commodity underlying the contract. Rather, the contract is based 
on the value of the S&P 500 stock index. At the expiration of the contract, each open 
contract is marked to market at the closing price of the S&P 500 stock index and dis­
appears. All contracts are settled for cash on their final day and then they no longer 
exist - they expire. The terms of the contract specify that each point of movement is 
worth $250. Thus, if the S&P 500 Index itself is at 1405, then the S&P futures con­
tract is a contract on $250 x 1405, or $351,250 worth of stocks comprising the index. 
Assume the initial margin for one of these contracts is $30,000, although it may vary 
at specific brokerage houses. 
Suppose that a trader buys one December S&P futures contract for his account 
sometime in October. With the underlying index at 1405.00, suppose he pays 1417.50 
for the futures contract. It is normal for the futures to trade at a premium to the actu­
al index price. The reasons regarding this will be discussed in a later section. Initially, 
the customer puts up $30,000 as margin, and this may be in the form of T-bills. On 
the next day, however, the market declines and the futures close at 1406.00. This rep­
resents a loss of 11.50 points from the purchase price. At $250 per point, the trader 
has a loss of $2,875 (250 x 11.50) at this time. He is required to add $2,875 in cash 
into the account.