Source: European Union, 2010
The level is about twice that previously estimated and is likely to cheer advocates of the movement to make the results of publicly-funded research freely available.
According to the study – published on 21 August by Montreal-based research evaluation consultancy Science-Metrix – Brazil, Switzerland, the Netherlands and the US have the highest rates of open access publishing.
In Europe, 20 out of countries, including the UK, are likely to have tipped towards a majority of papers published in 2008-2011 being made available for free, it adds.
Articles in biomedicine, biology, and mathematics and statistics were the most likely to be free to access, while the lowest rates were in the social sciences and humanities, applied sciences, engineering and technology.
The report also found that more than 40 per cent of scientific peer-reviewed articles published worldwide from 2004 to 2011 are now available online in open-access form.
The authors of the study put the big increase on previous estimates down to a refined methodology and wider definition of open access.
They derived their figures by randomly sampling 320,000 papers from the database Scopus, published in 22 fields between 2004 and 2011, then searching online in repositories, publisher websites and institutional archives for the full texts.
The European Commission, which funded the study, said it demonstrated that a “tipping point” in open access publishing has been reached.
Máire Geoghegan-Quinn, commissioner for research, innovation and science, said: “Putting research results in the public sphere makes science better and strengthens our knowledge-based economy.”
From 2014, the EU body expects publication of all the research it funds to be open access – either through “gold” or “hybrid” models, with any upfront publisher costs eligible for reimbursement; or through the “green” self-archiving model no later than six months after publication, or 12 months for social sciences and humanities papers.
In the UK, open access publishing is already mandatory for papers funded by a number of funders including the research councils and Wellcome Trust, although policies and levels of compliance vary.