I have never had a margin sellout, but a friend asked me a question that I do not have an answer. Say you own 1000 shares of a stock on margin that has gone down enough to be in a margin call situation. I know that IB automatically sells you out, but how much do they sell? Do they sell just enough to get back within maintenance margin requirements, initial margin requirements, or the whole position? Do they sell odd lot amounts, say 512 shares. How does all this work?