International audience; Quantitatively assessing seismic attenuation caused by fluid pressure diffusion (FPD) inpartially saturated rocks is challenging because of its sensitivity to the spatial fluid distribution. To addressthis challenge we performed depressurization experiments to induce the exsolution of carbon dioxidefrom water in a Berea sandstone sample. In a first set of experiments we used medical X-ray computedtomography (CT) to characterize the fluid distribution. At an equilibrium pressure of approximately1 MPa and applying a fluid pressure decline rate of approximately 0.6 MPa per minute, we allowed achange in saturation of less than 1%. The gas was heterogeneously distributed along the length of thesample, with most of the gas exsolving near the sample outlet. In a second set of experiments, at thesame pressure and temperature, following a very similar exsolution protocol, we measured the frequencydependent attenuation and modulus dispersion between 0.1 and 1,000 Hz using the forced oscillationmethod. We observed significant attenuation and dispersion in the extensional and bulk deformationmodes, however, not in the shear mode. Lastly, we use the fluid distribution derived from the X-ray CTas an input for numerical simulations of FPD to compute the attenuation and modulus dispersion. Thenumerical solutions are in close agreement with the attenuation and modulus dispersion measuredin the laboratory. Our approach allows for accurately relating attenuation and dispersion to the fluiddistribution, which can be applied to improving the seismic monitoring of the subsurface.