  We report electronic transport experiments on a graphene single electron
transistor. The device consists of a graphene island connected to source and
drain electrodes via two narrow graphene constrictions. It is electrostatically
tunable by three lateral graphene gates and an additional back gate. The
tunneling coupling is a strongly nonmonotonic function of gate voltage
indicating the presence of localized states in the barriers. We investigate
energy scales for the tunneling gap, the resonances in the constrictions and
for the Coulomb blockade resonances. From Coulomb diamond measurements in
different device configurations (i.e. barrier configurations) we extract a
charging energy of 3.4 meV and estimate a characteristic energy scale for the
constriction resonances of 10 meV.
