Abstract: A fully-parallelized, highly-efficient compositional implicit hydrocarbon reservoir simulator is provided. The simulator is capable of solving giant reservoir models, of the type frequently encountered in the Middle East and elsewhere in the world, with fast turnaround time. The simulator may be implemented in a variety of computer platforms ranging from shared-memory and distributed-memory supercomputers to commercial and self-made clusters of personal computers. The performance capabilities enable analysis of reservoir models in full detail, using both fine geological characterization and detailed individual definition of the hydrocarbon components present in the reservoir fluids.