Electronic Journal of Differential Equations, Conference 02 (1999), pp. 29-46. Title: Degenerate two-phase incompressible flow problems III: Perturbation analysis and numerical experiments Authors: Zhangxin Chen (Southern Methodist Univ., Dallas, TX, USA) Natalia L. Khlopina (Southern Methodist Univ., Dallas, TX, USA) Abstract: This is the third paper of a three-part series where we develop and analyze a finite element approximation for a degenerate elliptic-parabolic partial differential system which describes the flow of two incompressible, immiscible fluids in porous media. The approximation uses a mixed finite element method for the pressure equation and a Galerkin finite element method for the saturation equation. It is based on a regularization of the saturation equation. In the first paper \cite{RckA} we analyzed the regularized differential system and presented numerical results. In the second paper \cite{RckB} we obtained error estimates. In the present paper we describe a perturbation analysis for the saturation equation and numerical experiments for complementing this analysis. Published December 9, 1999. Math Subject Classifications: 35K60, 35K65, 76S05, 76T05. Key Words: porous medium; degenerate elliptic-parabolic system; perturbation method; finite element; regularization; two-phase flow.