The Monte Carlo method was used to simulate particle segregation in gravitational fields. Systems containing one or two types of spherical particles were simulated, assuming that the particles interact according to a quasi-hard core potential. Systems with 1000 particles were simulated, replicated by periodical boundary conditions in the directions perpendicular to the gravitational field; at the top and bottom of the simulation box, the existence of rigid walls was assumed. Results for local composition and local voidage as a function of the height of the solid sediment are presented. The results for binary systems show that when very light particles are present in the mixture, it is possible, under certain conditions, to obtain configurations in which the particles with the smallest diameter concentrate at the top of the solid sediment. In order to observe the three-dimensional system configurations that result from the simulations, computational programs were developed in the virtual reality modeling language (VRML).