  In this article we try to find out the conditions when a ghost field in
conjunction with a barotropic fluid produces a stable accelerating expansion
phase of the universe. It is seen that in many cases the ghost field produces a
condensate and drives the fluid energy density to zero in the final
accelerating phase, but there can be other possibilities. We have shown that a
pure kinetic $k$-essence field (which is not a ghost field) interacting with a
fluid can also form an interaction induced condensate and produce a stable
accelerating phase of the universe. In the latter case the fluid energy density
does not vanish in the stable phase.
