  We establish 2-jet determinacy for the symmetry algebra of the underlying
structure of any (complex or real) parabolic geometry. At non-flat points, we
prove that the symmetry algebra is in fact 1-jet determined. Moreover, we prove
1-jet determinacy at any point for a variety of non-flat parabolic geometries -
in particular torsion-free, parabolic contact, and several other classes.
