Experimental values for the vibrational Gr¿neisen ratio, &ggr;v, for hexagonal close-packed (hcp) iron, called epsilon (&egr;)-iron, were obtained over a large compression range corresponding to Earth's inner-core pressure. This was done by measuring the intensity change in x-ray diffraction lines under pressure, P. X-ray structural refinement using the Rietveld method on powder diffraction data yielded information on mean square displacement used to obtain the Debye temperature, &THgr;, as a function of compression, V/V0. The value of &THgr; was determined from the measured intensity of the diffraction lines, which arises from the mean squared amplitude ⟨u2⟩ measured in-situ in the diamond cell. From the Debye relationship, &ggr;v=-(∂ln &THgr;/∂ln V)T, we determined experimental data on &ggr;v versus V of Fe (hcp) up to 330 GPa at 300 K. The measured value of &ggr;v(V) is 1.18 at 330 GPa and 1.41 at 135 GPa. ¿ 2001 American Geophysical Union