The application of continuous-mixture thermodynamics for representing the hydrocarbon phases in a compositional reservoir simulator is considered as opposed to the conventional approach which uses several discrete pseudocomponents to characterize the phases. A method of formulating the continuous material balance and phase equilibrium relationships within an implicit pressure-explicit saturation (IMPES) framework is demonstrated. A one-dimensional reservoir simulator was written, and continuous-mixture thermodynamics was successfully employed. The results obtained from the continuous and the discrete versions of the simulator are in good agreement for the test cases considered.