  Overlay journals are characterised by their articles being published on open
access repositories, often already starting in their initial preprint form as a
prerequisite for submission to the journal prior to initiating the peer-review
process. In this study we aimed to identify currently active overlay journals
and examine their characteristics. We utilised an explorative web search and
contacted key service providers for additional information. The final sample
consisted of 34 overlay journals. While the results show that new overlay
journals have been actively established within recent years, the current
presence of overlay journals remains diminutive compared to the overall number
of open access journals. Most overlay journals publish articles in natural
sciences, mathematics or computer sciences, and are commonly published by
groups of academics rather than formal organisations. They may also rank highly
within the traditional journal citation metrics. None of the investigated
journals required fees from authors, which is likely related to the
cost-effective aspects of the overlay publishing model. Both the growth in
adoption of open access preprint repositories and researchers' willingness to
publish in overlay journals will determine the model's wider impact on
scholarly publishing.
