the key is the 17 cent a trade. the note from 2002 is correct. penson has something called batch clearing thats why swift gets there guys to hit in and out of a few stocks all day long. penson charges 1 small fee per stock per day. they might charge 35 cents for each trader that trades aapl. so if i trade 100k shares of aapl thats 35 cents commission per day and they charge me 17 cent a trade.try trading 500k shares at .003 plus sec fee's. you're talking 2k a day of commissions which you'll never overcome. man those fat ass company's like amtd trading $10 a trade are killing it. also remember these ecn rebates. all these prop house are screwing people charging .0005 to use nyfix or other sdot routers plus if a firm like hold is trading 20 million or more a day on inet there's some extra rebates not being passed to most traders. everyone's screwing the heavy trader