Over the past three decades, the share of Tunisia's output of fruits and vegetables passing through the capital's wholesale market has declined sharply. One reason is that, following the formation of a porters' cooperative, the cost of portage services and, hence, that of using the market has skyrocketed. In advancing this argument, the paper explores how the cooperative has managed to maintain a monopoly over portage services despite widespread dissatisfaction with its performance. In addition, it offers some thoughts on the distributional and efficiency implications of various changes engendered by the cooperative in the market's mode of operation.