A computer code was developed for numerical simulation of two-phase flow in porous media considering mass transfer between the phases involved and solute transport in each phase. Enhanced mobility of nonaqueous phase and enhanced aqueous solubility of its components as a result of cosolvent injection are calculated. The objective of this work was to simulate subsurface contamination by nonaqueous phase liquids and remediation utilizing cosolvent injection technique, and also contamination by gasoline with alcohol from fuel tanks. It is also possible to solve two-phase flow problems involving a gaseous phase. A model for mass transfer during two-phase flow was developed and implemented. Properties variation with time for both phases is calculated using ternary phase diagram. Finite element method was used to solve flow and solute transport equations.