Dark energy and viscous cosmology

Singularities in the dark energy universe are discussed, assuming that there is a bulk viscosity in the cosmic fluid. In particular, it is shown how the physically natural assumption of letting the bulk viscosity be proportional to the scalar expansion in a spatially flat FRW universe can drive the fluid into the phantom region ( w < -1), even if it lies in the quintessence region ( w > -1) in the non-viscous case.