The calculations of the P-V isotherms of fluid hydrogen isotopes H2 , D2 , and T2 up to their freezing pressures at 200, 300 and 500 K have been performed for 4 kinds of intermolecular potentials by using the modified hard-sphere variational perturbation theory with a quantum correction. By comparing the results with the 300 K experimental equation of state, it has turned out that the agreement is good for the potentials of Silvera-Goldman and Nellis et al. except near the freezing point of H2 . The quantum pressures were estimated, and their dependences on volume, molecular mass, and temperature are discussed quantitatively. We discuss the discrepancy of the P-V isotherms between experiments by Brillouin scattering and theoretical results for H2 near the freezing point, including the recent solid isotherms to higher pressures.