The lattice parameter of magnesiowfistite (Mgo.6Feo.~)O has been measured up to a pressure of 30 GPa and a temperature of 800 K, using an external heated diamond anvil cell and diffraction using X-rays from a synchrotron source. The experiments were conducted under quasi-hydrostatic condition, using neon as a pressure transmitting medium. The experimental P-V-T data were fitted to a thermal-pressure model with the isothermal bulk modulus at room temperature Kro = 157 GPa, (•Kro/OP)T=4, (~KT/OT),: -2.7(3)
• 10 .2 GPa/K, (~KT/OT),= -0.2(2)x 10 -2 GPa/K, and the Anderson-Grfineisen parameter 6T=4.3(5) above the Debye temperature. The data were also fitted to the Mie-Griineisen thermal equation of state. The least-squares fit yields the Debye temperature 0Do =500(20) K, the Griineisen parameter 7o= 1.50(5), and the volume dependence q = 1.1 (5). Both thermal-pressure models give consistent P-V--T relations for magnesiowfistite to 140 GPa and 4000 K. The P-V-T relations for magnesiowiistite were also calculate by using a modified high-temperature Birch-Murnaghan equation of state with a 6T of 4.3. The results are consistent with those calculated by using the thermal-pressure model and the Mie-Griineisen relation to 140 GPa and 3000 K.