Another poster posts... "Long answer is that what

Another poster posts...

"Long answer is that what he means by cost prohibitive is the margin requirements. For example at the broker that I use, you have to have $2.50 margin per share to short a stock under $2.50. So if you short 1000 shares of a stock at $2, you have to have $2,500 in your account ($2.50 x 1000). If you want to short 1million shares of a stock at .0001, you have to have $2.5mllion in your account, and 1million shares at .0001 is only $100. So it wouldn't make sense to do. The bright side is that if you do short something down there, you won't get a margin call unless it exceed $2.50, which isn't very likely for a .0001 stock. But again, you'd never short $100 worth of a penny stock if you had $2.5 mil in your account."