Abstract:  While guest or honorary authorship on academic papers is a broadly and widely discussed phenomenon in biomedical research, the issue of the use – or abuse – of article processing charges (APCs) as a form of potential authorship exchange currency, i.e., the “APC ring”, is not being discussed. The APC is central to the open access (OA) movement, specifically gold OA, including hybrid subscription models. It is conceivable that poorly-funded researchers aiming to publish in ranked (e.g., with a Clarivate journal impact factor or indexed in a major database such as Scopus) OA journals with expensive APCs (sometimes costing thousands of US dollars or Euros) might turn to richer researchers to foot the bill in exchange for authorship. Despite this, extensive web and database searches revealed no published cases on APC-for-authorship schemes as a form of guest authorship, which seems inconceivable. One possible explanation is that if such unethical behavior, and a form of fraud, were to be detected by APC-charging journals, that it might not be reported as such. Alternatively, if it has been detected as such, it might be reported (e.g., to the public) more broadly as “authorship issues” without detailing that an APC-based guest authorship scheme (i.e., “APC ring”) was involved. In such a situation, APC-dependent journals would be conflicted between receiving a financial lifeline, the APC, and exposing authors that abuse the APC in exchange for authorship. How would OA publishers justify receiving APCs derived from an “APC ring”? Although this form of guest authorship is currently hypothetical, it is also highly likely, so this issue needs greater debate. If actual case studies exist, these need to be openly and publicly debated to better appreciate how widely this phenomenon may be taking place.