A detailed study investigates the effects of an acoustic logging tool (modeled as rigid) on the propagation characteristics of Stoneley waves in both elastic and porous boreholes. In an elastic borehole, the presence of the tool reduces the Stoneley velocity and enhances the Stoneley wave excitation. When intrinsic attenuation resulting from formation and borehole fluid inelasticity is present, the tool reduces Stoneley attenuation from the fluid and increases the attenuation from the formation. For a permeable porous borehole, the simplified Biot-Rosenbaum model of Tang et al. (1991) is modified to incorporate the effects of the tool on the Stoneley propagation. On the basis of the formulation for the elastic formation, a simple, effective method is presented for calculating the Stoneley wave excitation in a porous borehole. During acoustic logging in a porous formation, the Stoneley wave amplitude is affected by both the permeability of the formation and other factors unrelated to permeability. The latter effects include wave excitation due to the elastic properties of the porous formation and the transmission and reflection at bed boundaries. Using the results of this study, the nonpermeability effects can be separated from the permeability effects, which is demonstrated using a synthetic Stoneley wave log across a porous zone.