  We present the perturbative (PT) and non-perturbative (NP) analysis of the
cumulative out-of-event-plane momentum distribution in e+e- annihilation in the
near-to-planar three-jet region. A physical interpretation based on simple QCD
considerations and kinematical relations will be given, with the aim of
extending the described techniques to other multi-jet processes and, possibly,
to hadron-hadron collisions.
