Update: please note that the estimate of 9.3% are the articles in fully gold journals. The number of OA articles including hybrid journals, and numbers of articles that become OA only after an embargo or delay, is not included in this number.
About 9.3% of the world's peer-reviewed journal articles are now fully gold! This is double the number reported for 2006. Another sure sign of the Dramatic Growth of Open Access!.
Björk et al. (2008) calculated that of the estimated 1,350,000 journals articles published in 2006, 19.4% are freely accessible (4.6% OA immediately on publication, 3.5% freely accessible after an embargo, usually at least on year; and 11.3% through self-archiving).
From: Björk, Bo-Christer, Annikki Roosr, and Lauri, Mari. Global annual volume of peer reviewed scholarly articles and the share available via different open access options. ELPUB2008. Open Scholarship: Authority, Community, and Sustainability in the Age of Web 2.0 - Proceedings of the 12th International Conference on Electronic Publishing held in Toronto, Canada 25-27 June 2008 / Edited by: Leslie Chan and Susanna Mornati, 2008, pp. 178-186.
DOAJ currently lists 3,653 journals, about 15% of the world’s peer-reviewed scholarly journals, and is adding new titles at a rate of more than 2.2 per calendar day. If we multiply the number of journals in DOAJ (3,653) by the mean number of articles / OA journal calculated by Björk et al. (2008), of 34.6, we get an estimated total number of articles that are fully OA of 126,393, 9.3% of the total estimated output of 1,350,000 estimated by Björk et al., or twice as much fully gold OA now as there was in 2008.
Please note that this is a rough estimate. The 1.35 million articles per year has likely increased by about 7-8%, based on average increases of about 3-3.5% per year. This figure has not been changed for the estimate, as the 34.6 articles / OA journal may also have changed; it is possible that the average number of journals per article has increased as awareness of open access increases, and as some of the OA journal start-ups have been around for a while and are beginning to attract more submissions.
Apologies to e-mail subscribers for the duplication; I accidentally posted two versions of this in draft.