Spontaneous inter-particle percolation is a mechanism of particle segregation which arises when a particle falls through the voids among large particles due to gravity or other applied force, the size difference being such that this can occur without the need for applying strain. It is a phenomenon arising in some packed bed processing operations and in some dispersers for particles. Here the mechanism is modelled by computer simulation. The model uses particle sizes, a coefficient of restitution and also, to cater for less elastic materials, a coefficient of friction. This yields percolation velocities quantitatively consistent with prior laboratory studies, showing the correct dependence on coefficient of restitution and particle size. The simulation clarifies the dependence of radial dispersion on packing height. The radial distributions are well described only at higher coefficients of restitution, pointing to the need for a better means of describing collisions between percolating and packed particles. (C) 2010 Elsevier B.V. All rights reserved.