Push back pallet rack systems offer similar storage density as drive-in pallet rack while improving selectivity and accessibility to a range of SKUs. Product stored in lanes rests on a system of carts-on-rails available in 2 to 6 pallets deep. From one aisle, pallets are stored by "pushing back" previously placed pallets with a new pallet on the next cart position. When the front pallet is retrieved, gravity causes the next pallet to move forward into a ready position. This "last-in, first-out" system (per lane) reduces picking time when a large number of picking faces are required.