We present a generalized BCS analysis of a liquid of excitons having t
wo different spin orientations. Both the energy and the chemical poten
tials of this system depend strongly on both the spin polarization P a
nd total density n. When electrons and holes are located in two differ
ent planes separated by a distance d, the liquid can be either totally
spin polarized for d > d(cr)(n) or spin unpolarized (d < d(cr)(n)). T
he phase coherence induced by exciton condensation is discussed.