Seasonal oligopoly power: the case of the US fresh fruit market

What has been ignored in much of the existing studies of oligopoly power is that market behaviour need not be static in nature, and oligopoly power in agriculture need not be present in every month of the year. In a market which is characterized by seasonality and supplied by different sources during different seasons, it is quite possible to observe oligopoly power during different months of the year. In this paper, a method for estimating and testing for seasonal changes in the degree of oligopoly power is introduced. It was found that in the pear market, oligopoly power coefficients remain low throughout the year. On the other hand, the grape market is characterized by higher oligopoly power coefficients and considerable season variations.