  We calculate thermodynamic quantities in symmetric nuclear matter within the
self-consistent Green's functions method including three-body forces. The
thermodynamic potential is computed directly from a diagrammatic expansion,
implemented with the CD-Bonn and Nijmegen nucleon-nucleon potentials and the
Urbana three-body forces. We present results for entropy and pressure up to
temperatures of 20 MeV and densities of 0.32 fm^-3. While the pressure is
sensitive to the inclusion of three-body forces, the entropy is not. The
unstable spinodal region is identified and the critical temperature associated
to the liquid-gas phase transition is determined. When three-body forces are
added we find a strong reduction of the critical temperature, obtaining T_c ~
12 MeV.
