We use panel data from two experiments conducted five months a part to investigate the stability of individual preferences and aggregate demand for five types of fish. Even though the bids in the two experiments are positively correlated, they clearly suggest that the individual preferences are unstable. This may be explained by internal desire for variety or by external effects such as new relevant information, seasonality in preferences, changes in the quality of the fish, and changes in the market price of fish. However, the aggregate demand curves of the participants are stable when we control for changes in the perceived quality of the fish and price expectations of the participants. In other words, the stability is generated by aggregation rather than derived from stable individual preferences.