This study aims to estimate the total amount of article processing charges (APCs) paid to publish open access (OA) in journals controlled by the large commercial publishers Elsevier, Sage, Springer-Nature, Taylor & Francis and Wiley, the so-called oligopoly of academic publishing. Since the early 2010s, these five academic publishers control more than half of peer-reviewed journal articles indexed in the Web of Science (WoS), expanding their market power through acquisitions and mergers. While t...