Abstract: An adjustable depth shelf mechanism comprises a fixed shelf mountable on a vertical support mechanism, an adjustable shelf mounted on the fixed shelf for inward and outward movement on the fixed shelf to vary the depth of the shelf, and locking means for holding the adjustable shelf in one or more extended positions with respect to the fixed shelf. The shelves comprise wire mat product support surfaces mounted on shelf brackets. The wire mats include longitudinal wires on top of transverse wires. Downwardly extending notches are formed in the transverse wires of the fixed shelf at positions corresponding to the desired extended positions. The longitudinal wires of the adjustable mat fit into the notches when the adjustable mat is at the desired extended positions, such that the adjustable shelf mat lockingly nests in the fixed shelf mat and the shelves present a substantially coplanar upper surface.