  We consider the background of a rotating axially symmetric black hole. Let
particle 0 decay to two fragments 1 and 2 in the direction parallel to that of
particle 0. It is shown that if decay occurs inside the ergoregion, both
particles 1 and 2 move in the same direction as particle 0. For the scenario,
when decay happens in the turning point of all three particles, we find the
condition when angular momenta of both particles 1 and 2 have the same sign. We
elucidate the relation between the approach of Wald that imposes constraint on
maximum and minimum energies of fragments and our approach. In doing so, we
express the results in terms of characteristics of particle 0 and all particle
masses. The conditions of the maximum efficiency depending on the relation
between masses is discussed. We find an explicit expression for angular momenta
of particles 1 and 2. We discuss also particle decay for static black holes,
when the Penrose process is impossible. Because of the absence of the
ergoregion in the static case, scenarios of decay for static black holes can
significantly differ from those in the rotating background.
