A key parameter in any discussions about the academic peer reviewed journal system is the number of articles annually published. Several diverging estimates of this parameter have been proposed in the past, and have also influenced calculations of the average production price per article, the total costs of the journal system and the prevalence of Open Access publishing. With journals and articles increasingly being present on the web and indexed in a number of databases it has now become possible to quite accurately estimate the number of articles. We used the databases of ISI and Ulrich’s as our primary sources and estimate that the total number of articles published in 2006 by 23 750 journals was approximately 1 350 000. Using this number as denominator it was also possible to estimate the number of articles which are openly available on the web in primary OA journals (gold OA). This share turned out to be 4.6 % for the year 2006. In addition at least a further 3.5 % was available after an embargo period of usually one year, bringing the total share of gold OA to 8.1% Using a random sample of articles, we also tried to estimate the proportion of the articles published which are available as copies deposited in e-print repositories or homepages (green OA). Based on the article title a web search engine was used to search for a freely downloadable full-text version. For 11.3 % a usable copy was found. Combining these two figures we estimate that 19.4 % of the total yearly output can be accessed freely.

*Global annual volume of peer reviewed scholarly articles and the share available via different open access options*." In

*Sustainability in the Age of Web 2.0 - Proceedings of the 12th International Conference on Electronic Publishing*, 178-186. ELPUB. Toronto, Canada, 2008.