Discharge of a cohesive bulk solid from a plug-flow bin is (too) often interrupted by the development of a stable channel within the bulk solid. In this article, various methods to determine critical outlet dimensions to avoid channeling are reviewed critically and compared with the results of experiments. It is shown that the results of these methods vary between an underestimation and an extreme overestimation of the critical outlet dimensions. Experiments have been performed using different bins and bulk solids. In contrast to what is generally assumed, these experiments showed that critical outlet dimensions for arching can be larger than those for channeling. It also appeared that fitting a smooth hopper underneath a bin results in a smaller critical outlet than a flat bottom.