  We present results from a fully relativistic Monte Carlo simulation of
diffusive shock acceleration (DSA) in unmodified shocks. The computer code uses
a single algorithmic sequence to smoothly span the range from nonrelativistic
speeds to fully relativistic shocks of arbitrary obliquity, providing a
powerful consistency check. While known results are obtained for
nonrelativistic and ultra-relativistic parallel shocks, new results are
presented for the less explored trans- relativistic regime and for oblique,
fully relativistic shocks. We find, for a wide trans-relativistic range
extending to shock Lorentz factors >30, that the particle spectrum produced by
DSA varies strongly from the canonical f(p) proportional to p^{-4.23} spectrum
known to result in ultra-relativistic shocks. Trans- relativistic shocks may
play an important role in gamma-ray bursts and other sources and most
relativistic shocks will be highly oblique.
