The measurement from borehole sonic data of Q, the acoustic attenuation coefficient of an earth section, can be achieved in three ways: forward modeling (Chuen and Toksoez, 1981), spectral ratios (Gladwin and Stacey, 1974), and inversion (Cheng et al., 1986). The spectral-ratio technique has been applied to real data (Goldberg et al., 1985) but is unstable and not very reliable. Experiments have shown that the spectral-ratio technique applied to waveforms gives Q estimates which are lower than those measured from cores in the laboratory (Goldberg and Zinszner, 1989). We investigate this phenomenon using synthetic and real data.