This paper presents the findings of an experimental investigation into size segregation in a 200 mm diameter batch jig that was conducted to provide background information for the development of a stratification model that accounts for the effects of both particle size and particle density on separation performance. The investigation focused on a simple system in which the only variable was particle size; i.e. binary systems involving 50% mixtures of two differently sized spherical glass beads from 14 mm to 4 mm diameter in 2 mm increments. The density of all beads was 2520 kg/m(3). The study revealed four different types of size segregation patterns that may occur in a jig bed, and gave some indication of the factors that determine the transition from one type to another under the specific experimental conditions of the test work carried out It also developed a conceptual picture of the dynamics affecting size segregation in batch jigs operated under equilibrium conditions and highlighted three mechanisms: the interplay between stratification and dispersive processes; interstitial tricking of smaller particles; and convective remixing of smaller particles in the bed. Interpretation of the findings suggests a compositional regime where one segregation mechanism dominates, i.e. the stratification/dispersion interplay, and that our modelling efforts should concentrate on this mechanism and this regime. (C) 2016 Elsevier Ltd. All rights reserved.