Equation‐of‐state data were measured for liquid carbon dioxide and air shock‐compressed to pressures in the range 28–71 GPa (280–710 kbar) using a two‐stage light‐gas gun. The experimental methods are described. The data indicate that shock‐compressed liquid CO2 decomposes at pressures above 34 GPa. Liquid air dissociates above a comparable shock pressure, as does liquid nitrogen. Theoretical intermolecular potentials are derived for CO2 from the data. The calculated shock temperature for the onset of CO2 decomposition is 4500 K at a volume of 17 cm3/mol.