This paper presents numerical results on the development of compositional fluid mixing simulators in porous media. These simulators integrate geological processes (source rock maturation, hydrocarbon generation, migration, charge/filling, etc.) and reservoir processes (fluid mixing through Darcy's flow, advection, and diffusion, gravity segregation, etc.). The model governing equations are written with a proper choice of solution variables so that numerical mass conservation is preserved for all chemical components. The approximation procedure uses the finite volume method for space discretization, the backward Euler scheme in time, and an adaptive time stepping technique. The traditional simulator for solving the isothermal gravity/chemical equilibrium problem is deduced as a special example of the simulators presented here. Extensive numerical experiments are given to show segregation and instability effects for multiple components.