The application of phase plane analysis is extended on the basis of the authors’ previous paper in which this approach was suggested to analyze a set of first-order nonlinear ODE’s. The main point of phase plane analysis is the temporary elimination of non-intrinsic variables e.g. t and z, involved in the ODE sets which are commonly encountered in the course of solving reaction engineering problems. Two types of nonlinear ODE’s i.e. a set of firstorder ODE’s and a set of second-order ODE’s, which depict the phenomena of parametric sensitivity and multiplicity of reactors, respectively, are explained. The concept of iso-parameter lines of phase planes is taken advantage of, and, as a methodology, emphasis has been placed on the flexibility of phase plane analysis. The application of phase plane analysis is extended on the basis of the authors’ previous paper in which this approach was suggested to analyze a set of first-order nonlinear ODE’s. The main point of phase plane analysis is the temporary elimination of non-intrinsic variables eg t and z, involved in the course of solving reaction engineering problems. Two types of nonlinear ODE’s ie a set of firstorder ODE’s and a set of second-order ODE’s, which depict the phenomena of parametric sensitivity and multiplicity of reactors, respectively, are explained. The concept of iso-parameter lines of phase planes is taken advantage of, and, as a methodology, emphasis has been placed on the flexibility of phase plane analysis.