Joint purchasing can lead to the formation of buyer power. However, neither the phenomenon of buyer power itself nor its legal handling has been sufficiently clarified to date. One reason for this is the variety of possible economic impacts. These impacts are central to the question of whether purchasing cooperations restrict competition, especially in light of the 'more economic approach' now pursued by the European Commission. The work delves deeply into the Commission's guidelines on horizontal cooperation. In these guidelines, buyer power is the central criterion for the antitrust assessment of purchasing cooperations. Although the guidelines only partially meet the expectation for a detailed presentation and concrete legal classification of economic impacts, they largely reflect the Commission's approach in merger control procedures, thus providing important assistance for legal practitioners. Finally, the work aims to contribute to the fundamental question of whether the 'more economic approach' is justified, particularly concerning case law.