## Physics and Syntax

Presently, PorousFlow provides several Materials to model two-phase flow. However, all of the PorousFlow Kernels are designed to be used with an arbitrary number of fluid phases, so that additional phases can be included in PorousFlow by simply creating new Materials that provide properties for each phase.
Two-phase flow can be modelled using either formulations where porepressure of each phase are the nonlinear variables, or where porepressure and saturation of one phase are solved. These Materials calculate the pressure and saturation of each fluid phases, as well as all derivatives with respect to the PorousFlow variables.