Unlike most simulations [+], we run an actual order book.  You can very, very easily exhaust the shares available at the best bid or offer and experience price slippage.  Avoiding that is literally the goal of level two.<p>+ Most investment games generate a spot price by magic and let you transact at it as much as you want.  We have actual counter parties (bots) running their own strategies, the number, composition, and interaction of which determine the prices available.  This is complicated; most simulations abstract it away to focus on their particular areas of interest.  Having a nice crunchy view of market microstructure wrapped in an API is our interest; we in turn punted on a lot of other things.  A big one: many people interested in stock markets want to trade Google; Stockfighter doesn&#x27;t have Google but might have e.g. Amalgamated Tree Frog Airlines (ATFA), with a fake-but-almost-plausible market dynamic to it much of the time.