Thanks for your post here. Given the way you phrased the question I might suggest visiting this link to get an informed answer to your first question. <a href="http://en.wikipedia.org/wiki/Naked_short_selling" rel="nofollow" target="_blank">http://en.wikipedia.org/wiki/Naked_short_selling</a> As for answering your last question (How much?) That's what The OddsMaker, our event-based backtesting tool, is for. ;) <a href="http://www.trade-ideas.com/Path_OddsMaker.html" rel="nofollow" target="_blank">http://www.trade-ideas.com/Path_OddsMaker.html</a>