As a test problem to demonstrate our method, we consider a physical problem arising in the transient flow of gas through a semi-infinite porous medium. In the investigation of the unsteady flow of gas through a semi-infinite porous medium [16–19] initially filled with gas at a uniform pressure at time , the pressure at the outflow face is suddenly reduced from to ( is the case of diffusion into a vacuum) and is thereafter maintained at this lower pressure. The studies in [18, 20] show that the unsteady flow of gas in a porous medium is modeled by a nonlinear partial differential equation.