  We study transport through a double quantum dot, both in the sequential
tunneling and cotunneling regimes. Using a master equation approach, we find
that, in the sequential tunneling regime, the differential conductance
  $G$ as a function of the bias voltage $\Delta\mu$ has a number of satellite
peaks with respect to the main peak of the Coulomb blockade diamond. The
position of these peaks is related to the interdot tunnel splitting and the
singlet-triplet splitting. We find satellite peaks with both {\em positive} and
{\em negative} values of differential conductance for realistic parameter
regimes. Relating our theory to a microscopic (Hund-Mulliken) model for the
double dot, we find a temperature regime for which the Hubbard ratio (=tunnel
coupling over on-site Coulomb repulsion) can be extracted from $G(\Delta\mu)$
in the cotunneling regime. In addition, we consider a combined effect of
cotunneling and sequential tunneling, which leads to new peaks (dips) in
$G(\Delta\mu)$ inside the Coulomb blockade diamond below some temperature
scales, which we specify.
