I mostly trade Naz stocks and a couple futures and options. I have over the years tried ideas such as using gambling theory (pos-neg progressions) to try and get an edge. But what I've found, is that they may work if you are capitalized enough, but there are much better systems that show higher profit factor and much lower drawdown. Nobody ever said that using a martingale would not work, even on a neg expectation game (or trading system), IF you could take it to the extreme. But of course you will eventually run out of money or hit liquidity (table limit) plateaus first. These comments refer to trading a random entry, then progressing up-down until you get a profit. IOW no initial edge. If you start with a positive expectation system, then things get much easier. See 40yo's comments. FWIW an interesting book is Fortune's Formula. It over-hypes Kelly's, but is still interesting how so many Wall Street biggies and math wizards start out trying to beat Vegas. http://www.amazon.com/Fortunes-Formula-Scientific-Betting-Casinos/dp/0809046377 Good trading to all.