Expressions are derived for speed and attenuation of compressional waves travelling normal to the boundaries of a laminated medium which consists of alternating layers of two fluid-saturated porous solids. Fluid flow across boundaries is taken into account through approximate expressions, applicable at low frequencies, derived through extension of the approach used by Gassmann. Calculations show that when one of the saturating fluids is gas, substantial dispersion and extreme attenuation may result.