@Robert Morse, do you know if the rules permit rehypothecation only in the case of actual margin balances or also when you have levered complex positions. For example, suppose have an account with $100k in cash. Stock ABC is trading at $200 and you buy 10 ABC conversions with strike 100. Now you have no cash, $200k worth of ABC and -$100k in ABC synthetics. I've never been clear on whether shares of ABC are considered fully paid securities under Rule 15c3-3.