The degree to which scholarly journal articles published in subscription-based journals could be provided open access (OA) through publisher-permitted uploading to freely accessible web locations, so called green OA, is an underexplored area of research. This study combines article volume data originating from the Scopus bibliographic database with manually coded publisher policies of the 100 largest journal publishers measured by article output volume for the year 2010. Of the 1.1 million articles included in the analysis, 80.4 % could be uploaded either as an accepted manuscript or publisher version to an institutional or subject repository after one year of publication. Publishers were found to be substantially more permissive with allowing accepted manuscripts on personal webpages (78.1 % of articles) or in institutional repositories (79.9 %) compared to subject repositories (32.8 %). With previous studies suggesting realized green OA to be around 12 % of total annual articles the results highlight the substantial unused potential for green OA.