In this paper, it is demonstrated how a direct stiffness method for wa
ve propagation in multilayered saturated poroelastic media, based on i
ntegral transform techniques, can be modified to account for a small a
mount of gas in the pores, Unsaturated media with small gas fractions
can be treated using Smeulders' extension of Blot's poroelastic theory
. The effect of the presence of gas bubbles on the fluid bulk modulus
and the dispersion characteristics of a water-saturated sand of Mol is
demonstrated. The direct stiffness method is illustrated with a numer
ical example where transient wave propagation in a dry, saturated and
unsaturated halfspace is considered.