This chapter explores the minimal intelligence conditions for traders in a general double auction market with speculation activities. Using an agent-based model, it is shown that when traders and speculators play together under general market curve settings, zero-intelligent plus (ZIP) is still a sufficient condition for market prices to converge to the equilibrium. At the same time, market efficiency is lowered as the number of speculators increase. The experiments demonstrate that the equilibrium of a double auction market is an interactive result of the intelligence of the traders and other factors such as the type of the players and market conditions. This research fills in an important gap in the literature, and strengthens Cliff and Bruten’s (1997) declaration that zero is not enough for a double auction market.