We calculate the pressure (p), the energy density (\epsilon) and thebaryon density (n_B) of QCD at finite temperatures (T) and chemicalpotentials (\mu). The recently proposed overlap improving multi-parameterreweighting technique is used to determine observables at nonvanishingchemical potentials. Our results are obtained by studying n_f=2+1 dynamicalstaggered quarks with semi-realistic masses on N_t=4 lattices.