Whereas currently 617 Open Access (OA) journals were found to provide open peer review (OPR) options, journal publishers in medical and health sciences as well as natural sciences from Europe and India are leading in OPR adoption. The findings in this study indicate that the number of OA journals offering OPR has gone through an inflection point in 2017, when it stood at around 250. This number has, thus, increased by almost 250% by 2019, for which the latest data are available.

This paper also shows that in the domain of social sciences, in which the first OPR pilot was launched in 2001, in parallel to developments in medical and natural sciences, by 2019 the total number of journals providing OPR has remained relatively limited (n=50). This could be due to the largely optional nature of OPR among social sciences journals (60%). It stands in contrast to the sampled periodicals in medial and health sciences among which 64% mandate OPR.

This tentatively indicates that mandates facilitate OPR adoption.