  Starting with the Berlin declaration in 2003, Open Access (OA) publishing has
established a new era of scholarly communication due to the unrestricted
electronic access to peer reviewed publications. OA offers a number of benefits
like e.g. increased citation counts (Gargouri et al., 2010) and enhanced
visibility and accessibility of research output (Tennant et al., 2016). The OA
movement with its powerful mandating and policymaking has been very successful
in recent years. Relatively little is known about the real effects of these
activities in terms of OA publication output of institutions on a larger scale
(Piwowar et al., 2018). The aim of this article is to investigate to what
extent the OA fraction of the publication output of German universities has
increased in the last years. To answer this question, we analysed and compared
total number of publications which have been published by researchers of the
largest German universities. We compared the numbers of OA versus closed
publications for 66 large German universities in the time span of 2000-2017.
