INJECTION OF GAS SOLUTION IN RESERVOIRS HAVE RECEIVED A GREAT DEAL OF ATTENTION DURING MANY YEARS. FORTUNATELY, THERE ARE INCREASING NUMBER OF COMPOSITIONAL SIMULATORS TO SPECIFY ROCK AND FLUID VARIABLES IN DIFFERENT CONDITIONS; HOWEVER THIS PAPER DESCRIBES A SIMPLE AND NEW MATHEMATICAL MODELING BASED ON THE MULTIDIMENSIONAL COMPOSITIONAL EQUATIONS TO CHARACTERIZE THE RESERVOIR FLUIDS. THE MODEL TAKES INTO CONSIDERATION MASS CONSERVATION, DARCY'S EQUATION, COMPRESSIBILITY DEFINITIONS FOR ROCK AND FLUID, CAPILLARY PRESSURES AND DISPERSION OF COMPONENTS. THIS PAPER ANALYZES PRACTICAL ASPECTS OF COMPOSITIONAL MODELING THEORETICALLY. FINALLY, THE SIMULATION RESULTS ARE VALIDATED AGAINST A 2-D AND THREE PHASE FLOW IN A VAPOR EXTRACTION EXPERIMENT.