Sample of 3,730 journal articles published by authors from Catalonia's CERCA research centres between 2011 and 2015 and available on Web of Science (out of a total output of 44,423) identifying how many were available in open access, full-text format. The results revealed that 75,8% of the total (2,828 articles) had at least one version available in open access, but just 52% (1,940 articles) had at least one version available in either journals (whether pure or hybrid open access journals or those with embargo periods) or repositories, a finding that highlights the powerful role played by academic social networks in the sharp increase in open access availability. Of the 2,828 articles for which at least one open access version was found, a total of 9,868 copies were located. With respect to versions, the publisher’s final version, i.e. the type formatted for publication by journal publishers, was found in 75,3% of cases. The number of articles published in open access journals (567) was very close to the number of articles published in hybrid journals or journals with embargo periods (624). Only 40,4% of the articles in the sample were located in repositories, being the subject repositories the heaviest used. Fifty percent of the articles (1,881 publications) were posted on academic social networks, the most popular of which were ResearchGate and Academia. According to thematic areas, all six areas (science, life sciences, medical and health sciences, engineering and architecture and humanities) exceeded 70% of articles in open access.