  We study flux compactifications of 10d type II supergravities to 4d Minkowski
space-time, supported by parallel orientifold Op-planes with 3 $\leq$ p $\leq$
8. With some restrictions, the 4d Ricci scalar can be written as a negative sum
of squares involving BPS-like conditions. Setting all squares to zero provides
automatically a solution to 10d equations of motion. This way, we characterize
a broad class, if not the complete set, of Minkowski flux vacua. We also
conjecture an extension to include non-geometric fluxes. None of our results
rely on supersymmetry.
