This paper examines results on a series of Cournot markets with groups of five seller subjects. Step by step, we add complexity (and realism) to the simplest market and test the effects on behavior in an accompanying laboratory experiment. Consistent with previous experiments and the rational expectations hypothesis, price behavior was explained with Cournot Nash equilibrium with biases towards competitive prices. When complexity is increased, there rationality is degraded and lead to a salient cyclical tendency. Indications of cyclical behavior were induced by the application of spectral analysis and autocorrelation. We found that the more problematic effect of complexity in market behavior is the extra delay rather than accumulations. We proposed a heuristic based on the bounded rationality theory, but the tests were not satisfactory.