  We continue the investigations of lattice walks in the three dimensional
lattice restricted to the positive octant. We separate models which clearly
have a D-finite generating function from models for which there is no reason to
expect that their generating function is D-finite, and we isolate a small set
of models whose nature remains unclear and requires further investigation. For
these, we give some experimental results about their asymptotic behaviour,
based on the inspection of a large number of initial terms. At least for some
of them, the guessed asymptotic form seems to tip the balance towards
non-D-finiteness.
