The purpose of this paper is to present an analysis of a situation representative of oxygen diffusion in a soil profile where the soil water content is dependent on both depth and time. The appropriate governing differential equations and boundary conditions are presented for this situation. The solutions to the governing differential equations are in the form of numerical solutions in contrast to the analytical solutions presented in earlier studies. The resulting numerical solution method is applied to simulate the diffusion of oxygen in a draining soil profile which is initially completely saturated.