There are many types of open access, perhaps because it is such a young movement that it's still developing standards. That said, there are three basic types:
- Green – refers to self-archiving generally of the pre or post-print in repositories
- Gold – refers to articles in fully accessible open access journals
- Hybrid – some times called Paid Open Access, refers to subscription journals with open access to individual articles usually when a fee is paid to the publisher or journal by the author, the author's organization, or the research funder. Some of the fees are quite expensive, up to $5000. Some universities or libraries have a pool of funding available for hybrid journal publications or sometimes funding is written into grant applications for open access in hybrid journals, though these are not common instances. Some examples of hybrid open access are: iOpenAccess by Taylor Francis, Online Open by Wiley, or Sage Open by Sage.
Though green open access generally refers to the post-print of an article, there are three basic version types that can be self-archived in repositories:
- Pre-Prints – The author's copy of the article before it’s been reviewed by the publisher or pre-reviewed
- Post-Prints – The author's copy of the article after it’s been reviewed and corrected, but before the publisher has formatted it for publication, or post-reviewed.
- Publisher’s Version – The version that is formatted and appears in print or online.
If authors have signed a Copyright Transfer Agreement (CTA), the publisher's policy will determine which version of an article can be archived in a repository. Most publishers allow some sort of green open access. Authors can check their CTA for this information. SHERPA/RoMEO is a database of publisher copyright policies and self-archiving information that authors can use to check which version they may be allowed to archive. Not all journals are in SHERPA/RoMEO and it isn't always current, so authors may also want to check the publisher's website as well.
SHERPA/RoMEO classifies publishers into colors for easy identification:
- Green - refers to publishers whose policies allow archiving of pre-print and post-print or publisher's version/PDF
- Blue - refers to publishers whose policies allow archiving of post-print or publisher's version/PDF
- Yellow - refers to publishers whose policies allow archiving of pre-print
- White - refers to publishers whose policies do not formally support archiving any version
