Voids as probe of dark energy

Cosmological voids have the potential to be used as probes of the cosmological parameters. I will present our results on how sensitive some properties of voids, i.e. their ellipticies and number counts, are to the equation state of the dark energy. We used the Fisher matrix analysis to forecast the error bars on ``w'' using the void statistics combined with other cosmological probes to argue that the use of voids improves upon other probes with essentially no extra cost.