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. While traditionally their business model focused on subscriptions, they now increasingly charge fees for publishing. This study computes an estimate of the total amounts of APCs paid to oligopoly publishers between 2015 and 2018, using publication data from WoS, OA status from Unpaywall and annual APC prices from open datasets and historical fees retrieved via the Internet Archive Wayback Machine. We estimate that globally authors paid the oligopoly of academic publishers $1.06 billion in publication fees 2015-2018. Revenue from gold OA amounted to $612.5 million, while $448.3 million was obtained for publishing OA in hybrid journals, for which publishers already charge subscription fees. Among the five publishers, Springer-Nature made the largest revenue from OA ($589.7 million), followed by Elsevier ($221.4 million), Wiley ($114.3 million), Taylor & Francis ($76.8 million) and Sage ($31.6 million). With Elsevier and Wiley making the majority of APC revenue from hybrid fees and others focusing on gold, different OA strategies could be observed between publishers.

Version 2 of the preprint has been submitted to the journal Quantitative Science Studies.