PROPped up graph cohomology

We consider graph complexes with a flow and compute their cohomology. More specifically, we prove that for a PROP generated by a Koszul dioperad, the corresponding graph complex gives a minimal model of the PROP. We also give another proof of the existence of a minimal model of the bialgebra PROP from math.AT/0209007. These results are based on the useful notion of a 1/2 PROP introduced by Kontsevich in an e-mail message to the first author.