In this paper we briefly introduce the concept of Open Access and review the many variants that have been presented in the literature. We then critically examine how OA variants are presented by data source and how they are operationalized in practice. The goal of the paper is to provide a set of guidelines on how to effectively interpret OA information. To this end, we compare OA figures reported in different data sources at the institutional and journal level and dig into the potential explanations behind the differences observed on the figures each source provides.Policy highlightsOpen Access reporting in bibliometric reports is now possible due to the proliferation of data sources which provide information on the OA status of publications.Unpaywall has become the main primary source of OA metadata on publications for the main bibliometric databases, however there are divergences as to how these databases use and present data from this source.Understanding how OA variants are defined by each source and subsequently operationalized is key to correctly report and interpret Open Access uptake.