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.