This chapter describes the computational techniques commonly used in the simulation of supercritical extraction systems. Conventional Monte Carlo and molecular dynamics techniques are normally used to simulate supercritical phases for the purpose of gaining understanding and insight. Macroscopic property or behavior such as divergence in partial molar properties are traced to microscopic properties such as clustering at the molecular level. Specialized techniques designed for phase equilibria studies and the application of these techniques to a few model and real mixtures are described. Qualitative agreement with experimental results can be obtained when fairly simple effective potential models are used.