In this paper, we analyze successive oligopolies where downstream firms share the same decreasing returns technology of the Cobb-Douglas type. We stress the differences between the conclusions obtained under this assumption and those resulting from the traditional literature in which output firms use a constant returns technology. It is shown that when firms use a decreasing returns technology, (i) the profit of a downstream firm can decrease when the upstream market is more competitive; (ii) the input price does not tend to the corresponding marginal cost when the number of firms in both markets tends to infinite; and (iii) double marginalization is lower. Finally, the effects of mergers are revisited to highlight the role played by the technology of output firms.