  We present an N_t=4 lattice study for the equation of state of 2+1 flavour
staggered, dynamical QCD at finite temperature and chemical potential. We use
the overlap improving multi-parameter reweighting technique to extend the
equation of state for non-vanishing chemical potentials. The results are
obtained on the line of constant physics and our physical parameters extend in
temperature and baryon chemical potential upto \approx 500-600 MeV.
