Massively parallel supercomputers, such as the 150 Gigaflop Intel Paragons located at Oak Ridge National Laboratory and Sandia National Laboratories, make possible molecular simulation of systems of unprecedented complexity and realism. We describe some of the issues related to efficient implementation of molecular dynamics and Monte Carlo simulations on massively parallel supercomputers. The application of these methods to the prediction of the rheology of lubricants, polymer blends and high temperature aqueous electrolyte systems will be described.