  This study presents estimates of the global expenditure on article processing
charges (APCs) paid to six publishers for open access between 2019 and 2023.
APCs are fees charged for publishing in some fully open access journals (gold)
and in subscription journals to make individual articles open access (hybrid).
There is currently no way to systematically track institutional, national or
global expenses for open access publishing due to a lack of transparency in APC
prices, what articles they are paid for, or who pays them. We therefore curated
and used an open dataset of annual APC list prices from Elsevier, Frontiers,
MDPI, PLOS, Springer Nature, and Wiley in combination with the number of open
access articles from these publishers indexed by OpenAlex to estimate that,
globally, a total of \$8.349 billion (\$8.968 billion in 2023 US dollars) were
spent on APCs between 2019 and 2023. We estimate that in 2023 MDPI (\$681.6
million), Elsevier (\$582.8 million) and Springer Nature (\$546.6) generated
the most revenue with APCs. After adjusting for inflation, we also show that
annual spending almost tripled from \$910.3 million in 2019 to \$2.538 billion
in 2023, that hybrid exceed gold fees, and that the median APCs paid are higher
than the median listed fees for both gold and hybrid. Our approach addresses
major limitations in previous efforts to estimate APCs paid and offers much
needed insight into an otherwise opaque aspect of the business of scholarly
publishing. We call upon publishers to be more transparent about OA fees.
