Compositional simulators using an equation of state to describe the phase behavior of multicomponent fluid mixtures are expensive to use because of the large number of iterative phase equilibrium calculations and large computer storage space required. It is thus desirable to keep the number of components used in describing a fluid mixture to a minimum. This paper describes a method for reducing the number of components without a significant loss of accuracy in describing the phase behavior. Peng-Robinson equation-of-state models with up to five pseudocomponents were developed for three reservoir fluids ranging from a bubble-point to a dewpoint fluid under initial reservoir conditions. These models are shown to match the laboratory-measured phase behavoir data almost as accurately as the more complex 14 to 17 component models originally used in reservoir simulation.