The prediction of mineral liberation in mineral processing operations has become of major importance in the last two decades. This is especially the case for comminution processes. Many breakage liberation models have been proposed but none has focused on a particular form of breakage. Anecdotal evidence exists on the liberating qualities of particle bed breakage, however investigation of such qualities and their causes has been rarely performed. The paper describes work carried but in the development of a mineral liberation model for the particle bed breakage of a binary iron oxide ore. Confined particle bed breakage tests at various specific energies were performed on narrow grade fractions of a binary iron oxide ore. Liberation measurements of the resulting product size fractions were made by QEM*SEM. The Gay stereological correction method was applied to the measured areal distributions to obtain their volumetric form. With the liberation distributions from each size fraction it was possible to construct the conditional bivariate breakage function or Andrews-Mika diagram for each grade of particle. These bivariate breakage functions will be used in the prediction of the bivariate breakage functions resulting from the bed breakage of grade distributions. The liberation results, in conjunction with interfacial area measurements, provide evidence of the existence of two forms of non-random breakage; preferential breakage and interfacial breakage. It is the authors＇ contention that the former is promoted by the bed breakage mode. Selective liberation has ramifications for the random breakage assumption and the liberation models in which this assumption is used.