The information on thermodynamic properties of matter at extremely high pressures and temperatures is very important both for fundamental researches and applications. We have collected about 14000 experimental points on shock compression, adiabatic and isobaric expansion and measurements of sound velocities behind the shock front for more than 400 substances. The database with graphical user interface containing experimental data, approximation modules, and caloric equations of state models has been worked out. One can search the information in the database in two different ways and obtain the experimental points in tabular or plain text formats directly via the Internet using common browsers. Registered users can remotely add new data into the database. It is also possible to draw the experimental points on graphs in comparison with different approximations and results of equation‐of‐state calculations. Recently we have added an ability to make calculations of shock Hugoniots, isentropes, isobars, and other curves using semiempirical equations of state for more than 100 substances via the Internet. One can present the results of calculations in text or graphical forms and compare them with any experimental data available in the database. © 2004 American Institute of Physics