A package-culling conveyor system and a method for culling flat packages from a bulk flow of flat and non-flat packages. The conveyor system includes a tilted conveyor belt that conveys flat packages along its length while non-flat packages tumble off its lower side edge to initially cull flat packages from a bulk flow of packages. Retention means, such as a high-friction outer conveying surface or a raised barrier along the length of the outer conveying surface of the tilted conveyor belt, holds flat packages on the tilted conveyor belt. The initially separated packages are more fully culled in a conveyor comprising a roller conveyor belt with package-supporting belt rollers rotated in a direction to push packages sidewise toward a culling element that extends along the length of the roller conveyor belt. Examples of culling elements include powered rollers and vertical walls forming side guards. The powered roller lifts the contact side of non-flat packages to free flat packages underneath. The belt rollers push the flat packages under the culling elements and off the side of the roller belt. The culling elements block the non-flat packages from exiting laterally off the side of the roller belt so that they are conveyed off the exit end of the roller belt separate from the flat packages.