All references used for the included constants and temperature-dependent properties are available in the database file. In the xml file these are defined with the in line tag Comment for constants. For example the critical pressure of methane is defined as

citing the work of Twu and others(Ref. 8).

For temperature-dependent properties a separate <Comment></Comment> block is used.

The reference comments can be inspected in the settings window by right-clicking a species property node (under a Thermodynamic System) and selecting Properties.