The interior oil fraction in a microcapsule, defined as the ratio of the volume of oil isolated from the microcapsule surface to the whole volume of the microcapsule, was statistically calculated based on a two-dimensional percolation model. As the entire oil fraction increased, the interior oil fraction first increased and then sharply declined after reaching a maximum value. It was demonstrated that reduction of the oil-droplet size was effective in the preparation of microcapsules with a high interior oil fraction.