The applicabilities of Tait and Murnaghan equations of state and Bridgman polynomial to isothermal compressions of 10 polymer solids have been examined up to 3 GPa at room temperature. Tait and Murnaghan equations are equivalent and their linear forms (6) and (7) are very accurately for multisegmentally fitting the isothermal P-V date of amorphous

semi-crystaline polymer solids with the universal values CT= 0.0894 for Tait and CM= 0.1016 for Murnaghan parameter

Bridgman polynomial can also be used but is inconvenient when there are pressure-induced transitions. Equation is also presented for Gruneisen parameter from Tait and Murna-ghan parameters.