On Thurs 24 June I placed an order on my Comsec account to Sell to open 10 X BHPG48 (June 2010 39.50 puts- expiring same day). BHP at the time was about $39.80 and traded as low as, and closed at $39.65 that afternoon. My trading statement the following day showed selling 3 contracts to close and 7 to open, and also showed I had been assigned 3000 @ $39.50. I rang Comsec, but haven't received any explanation. My personal take on it is if I'm short puts they can be assigned at any stage, even at a price less than what the stock is trading for. However I'm not quite sure of the mechanics of assigning stock; for example, if there are numerous open interests, to whom does the stock get assigned. I'd appreciate some ideas.