The Internet has technically facilitated making scientific results available to a much wider readership than ever before, both via electronic subscriptions but also for free in the spirit of Open Source licensing of software and the knowledge sharing of Wikipedia. This emerging openness has important implications for better impact of published research in general and for bridging the digital divide between the researchers of the leading universities and the developing nations. A central question many policymakers ask is how common Open Access is today and how fast the share of OA is increasing. What proportion of journal articles are OA and to what extent do researchers post OA copies in repositories? Accurate answers to such questions would be very valuable for instance for research funders and for university administrators. The purpose of the study reported on in this paper is to provide answers to this type of questions.