This page lists some popular sites containing freely-available thermochemical databases. It is heavily biased towards inorganic chemistry and nuclear technology.
This listing should in no way be construed as an endorsement of the data by the OECD/NEA. The OECD/NEA makes no guarantee about the completeness and/or quality of the data in the databases listed here.
Available online from the NEA is also a brief survey of various thermochemical databases, which provides a bibliography of various databases that were published up until 1996.
Also, the University of Illinois at Chicago web site has an interesting page that contains many useful links to various sources of chemical data, not just thermodynamic.
Last reviewed: 13 December 2016