  We consider the harmonic measure on the Gromov boundary of a nonamenable
hyperbolic group defined by a finite range random walk on the group, and study
the corresponding orbit equivalence relation on the boundary. It is known to be
always amenable and of type III. We determine its ratio set by showing that it
is generated by certain values of the Martin kernel. In particular, we show
that the equivalence relation is never of type III_0.
