The P-V-T equation of state (EOS) of Pt has been determined to 80 GPa and 1900 K by in situ x-ray diffraction of a mixture of Pt and MgO using a modified internal resistive heating technique with a diamond anvil cell. The third-order Birch–Murnaghan EOS of Pt at room temperature can be fitted with K0=273.5±2.0 GPa, K0′=4.70±0.06, with V0=60.38 Å3. High temperature data have been treated with both thermodynamic and Mie–Grüneisen-Debye methods for the thermal EOS inversion. The results are self-consistent and in excellent agreement with those obtained by the multianvil apparatus where the data overlap. MgO is taken as the standard because its thermal EOS is well established and based on a wealth of experimental and theoretical data, and because the EOS at room temperature has been determined by a primary method that is completely independent of any assumptions or measurements by other methods. Improvements to previous internal resistive heating methods were made by using a Re gasket that replaces the original gasket composed of diamond and MgO powder. We have thereby extended the P-T range to nearly 80 GPa and 1900 K. Use of this method in combination with synchrotron radiation has advantages in the study of EOS, phase diagrams, and materials synthesis for a variety of problems in physics, chemistry, geosciences, and material sciences.