This book presents thermodynamic data on oxides in the system MgO-FeO-Fe₂O₃-Al₂O₃-SiO₂. These data are produced by a process of assessment that involves the integration of thermochemical (calorimetric) and phase equilibrium data. The latter have been selected from a number of publications in high-pressure research conducted at pressures and temperatures in the range of 1 bar to several Giga Pascals and 300 to 2500 K respectively. A unique feature of the database is that the assessment involves not only the thermodynamic data on pure end member species, but also the data on multicomponent solutions. Since the solution description follows the format used in the popular thermodynamic computational packages such as FACTSAGE, ChemSage and Thermocalc, the database is easy to incorporate in the currently used databases in these packages. The database is highly useful to those working in the field of metallurgy (e.g. slags) and ceramics. It is essential for all those who do thermodynamic modeling of the terrestrial planetary interiors.