The European Research Council has released Open Access Status of Journal Articles from ERC-Funded Projects.
Here's an excerpt:
The main objective of this analysis is to estimate the extent to which journal articles from ERC funded projects are available in an open access. . . .
The results show that 62 % of journal articles from ERC funded projects are available in open access. The share of articles in open access varies across research domains. It is close to 70 % in Life Sciences, 65 % in Physical Sciences and Engineering and nearer 50 % in Social Sciences and Humanities. A comparison with the data on open access status provided by the grant holders in their mid-term reports shows that self-reporting leads to an underestimation of the proportion of open access articles.