Just a few general questions on how brokers manage margin requirements when T-Bills are involved. Assume your brokerage lets you apply 100% of face value to margin requirements (no haircut). You open an account at XYZ Futures brokerage by depositing $10k in T-bills; you have no cash balance. You go long one ES (assume margin requirement $4000 initial/$3000 maintenance). a) Can you initiate that long position without having any cash balance? b) Next day, ES drops such that you incur a $1000 paper loss, but you're still comfortably within maintenance margin requirements. As I understand, your broker has to mark-to-market and settle with the exchange in cash at the end of each trading day, even though the position is open. Where does the $1000 in cash come from since you're physically invested in T-Bills? c) ES continues to drop, now you have a $2000 paper loss and decide to liquidate. What is standard operating procedure for the broker here - do they call you to cough up the cash, or do they just automatically "break" your T-bill position?