In an MOS transistor network, information can propagate through transistors and connections in both directions. Sometimes, however, it is intended to propagate in one direction only. Propagation in the wrong direction, causing a so-called sneak path, could result in a functional error. The author presents an almost linear algorithm for detecting such sneak paths. Only consistent sneak paths, i. e. , only paths that can possibly conduct, can cause a functional error; therefore, the algorithm allows inconsistent sneak paths to be left in the network. It does so without actually examining any paths, which would be too inefficient.