  We present a theoretical analysis of the normal and superfluid fractions of
quantum fluids described by a nonequilibrium extension of the Gross-Pitaevskii
equation in the presence of an external potential. Both disordered and regular
potentials are considered. The normal and superfluid fractions are defined by
the response of the nonequilibrium quantum fluid to a vector potential, in
analogy with the equilibrium case. We find that the physical meaning of these
definitions breaks down out of equilibrium. The normal and superfluid fractions
no longer add up to one and for some types of external potentials, they can
even become negative.
