In the aftermath of the '87, crash, I called my Refco broker and asked them "how they did"? Meaning, how much in the way of customer debits they might be facing? Refco said, "only about $300K, we think" (out of $20 Million company equity). They also said they'd rather customers not trade the SP contract at all (outcry pit, no ES at that time) until things settled down... and if I did want to trade the SP, Refco wanted $50K margin per contract.