A series of four experimental markets are described which examine the effect that different trading institutions have on sellers’ price expectations and market behavior. The results suggest that when sellers trade in information rich auction markets, their price expectations are relatively complex and adaptive. When sellers trade in more information poor posted price markets, their expectations are relatively simple and extrapolative. This difference in the complexity of expectations is reflected in the stability of the markets, the auction markets being more stable than the posted price markets. Overall the study supports the notion that trading institutions contribute to the observed complexity of price expectations.