This much is certain: there are most definitely traders so well-funded (for example, the JPMorgan Chase London Whale) that they can essentially... well, pretty much make the market move in whichever direction they deem appropriate/profitable with huge buy and/or sell orders. However, as explained today, there are limits to what a whale investor or trader can actually do. Anything from time-related limits (with it being multiple orders of magnitude easier for whales to manipulate short-term price movements than long-term ones) to many... you've guessed it, cons associated with being a whale trader/investor. Leaving conspiracy theories aside, this video explains that whale traders are large market participants without a doubt but at the end of the day, still market participants. Believe it or not, there are even instances in which a whale investor would love nothing more than for him or her to be an Average Joe investor, for example when trying to enter or exit a position in stealth move. As this video explains... there is more to whales than meets the eye, especially in the world of investing and trading :)