Abstract <p>One-sided density-driven convection in a porous medium is simulated numerically with reference to hydrodynamic processes occurring during injection of carbon dioxide into underground porous formations. When carbon dioxide dissolves in water or oil, the density of solution increases. This leads to the growth of instability. A hydrodynamic model that includes the continuity equation, the equation of motion (in the form of Darcy equation), and the convection-diffusion equation has been used. The equation of state that relates the density of the fluid phase to the concentration of carbon dioxide is nonlinear. The density of solution reaches a maximum at a certain concentration, which varies. A new computational code based on the finite-difference method has been developed to solve the problem. The effect of the concentration that gives the maximum density on the parameters of convective motion and mass transfer is investigated. In particular, it is found that if the maximum density occurs at a higher concentration, the amount of carbon dioxide that is transported downward by the convective flow increases. This means that, in this case, convective dissolution is more effective in trapping of carbon dioxide at depth.</p>