Sabena is of course correct. Forex along with global fixed income markets are the primary source of liquidity for funds, although the volatility of stock index futures certainly provides opportunity. But on balance Tudor Jones, Trout, Kovner ect. made the bulk of their money in Treasuries and or Forex. Don't completely write off equities though. Stocks still trade at higher vols then most anything else, and a talented trader can sacrifice short term liquidity concerns with the advantage of using capital to "goose" a company with i.e. a large short interest. You may be able to support your position in a lot of stocks, try doing that in $-Yen.