  Orbital Angular Momentum (OAM) twist-two parton distributions are studied. At
the low energy, hadronic, scale we calculate them for the relativistic MIT bag
model and for non-relativistic potential quark models. We reach the scale of
the data by leading order evolution using the OPE and perturbative QCD. We
confirm that the contribution of quarks and gluons OAM to the nucleon spin
grows with $Q^2$, and it can be relevant at the experimental scale, even if it
is negligible at the hadronic scale, irrespective of the model used. The sign
and shape of the quark OAM distribution at high $Q^2$ may depend strongly on
the relative size of the OAM and spin distributions at the hadronic scale.
Sizeable quark OAM distributions at the hadronic scale, as proposed by several
authors, can produce the dominant contribution to the nucleon spin at high
$Q^2$. As expected by general arguments, we obtain, that the large gluon OAM
contribution is almost cancelled by the gluon spin contribution.
